A Simpler Way to Calculate Global Oil Reserves?
Posted by Prof. Goose on September 13, 2006 - 12:14pm
As I recently re-read some articles on the debate about global oil reserves, a thought struck about how one could arrive at a rough estimate for such a number.
The search for that magic number of total oil in place and hence an estimate of how much can be realistically recovered has been a bone of contention across the Peak Oil divide. In fact, the absence or unreliability of data provides a sufficient haze for one group to point in one direction whilst another points in a completely opposite path. Hence we will find that estimates varying from 2 trillion barrels of URR up to 3 trillion barrels are the typical of the debate. Now a difference of one trillion barrels is important. At a current global consumption rate of 85 mbpd (original was 30 bbpd, that isn't right...PG) we get another 33 years of time to get things sorted out in terms of alternate energy sources and so on (though increasing demand would pull that number back to 20-25 years).
So I was considering the oil life of the United States of America...
In a moment of idle and lateral thinking, I wondered what the projected URR of the world would be if I just scaled up the projected URR of the USA to a global level? To put it another way, if you divide the land area of the world by the land area of the USA and multiply by the projected URR of the USA will you get a projected URR for the world?
Now I know this is not as subtle or complex as P5, P50, P95, Monte Carlo simulations or the work put in by analysts collating and adding up various oil projects across the world with the appropriate contingencies. It is not even as complicated as a Hubbert Linearization. But the possibility that a well-known and statistically significant area such as the USA may be a microcosm of world production intrigued me.
I needed just three numbers - the surface land area of the USA in square kilometres, the surface land area of the entire world in square kilometres and the estimated URR of the USA in gigabarrels.
The surface areas were obtained from Wikipedia and I excluded Antarctica from the total since it is effectively inaccessible.
Surface land area of USA: 9,631,420 sq km
Surface land area of World: 148,939,063 sq km minus Antarctica at 14,425,000 sq km = 134,514,063 sq km
The USA URR is taken from Colin Campbell's ASPO estimate of 195 billion barrels which can be found at this link.
So doing our division and multiplication gives a first approximation for world URR of 2.72 trillion barrels of oil. Remarkably this is very much in line with estimates calculated from more complex techniques and ironically finds itself half way between the estimates of the two divides of the Peak Oil controversy.
One or two things need to be said about this number. Firstly, one may dispute the USA URR itself and come up with different numbers. One for example may go for the fanciful USGS P50 estimate of 362 billion barrels and come up with a cornucopian number of 5.06 trillion barrels. This alone should suggest that the USGS estimate is way off the mark.
However, this projected world URR may in fact be overstating the actual numbers. I say this because no region of the world has been as thoroughly explored and drilled as the USA. It is unlikely that every country in every continent is going to receive the same degree of attention as the USA has had as the wealthiest nation in the world.
Also, what about offshore oil production which technically is not part of the land surface area? I took the line here that once again the USA was a microcosm of how world offshore URR would pan out. In terms of its share of global coastline, the USA has 19,924 km of coastline and the world has 292,643 km (after deducting for the Polar Regions - see link). This gives a ratio of 14.69 which compares well with our surface area ratios of 13.97.
So what can we say about our estimated world URR of 2.72 trillion barrels based on this simple approach? I for one take it as an upper limit on global oil reserves for reasons stated above. That takes it closer to the 2.1 to 2.3 trillion barrels normally quoted by Peak Oil experts than the 3 trillion expected by more optimistic analysts.
I say take it as it is, a rough calculation, but don't dispense with the more rigorous calculations that grace the Peak Oil debate today.
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Production versus reserves, again, I'm afraid. The global R/P ratio may be about 33 years but there will be reserves growth as there always is. This is the main Cornucopian argument. In terms of peak production, we have anywhere from 0 to 9 years left according to what I can figure out from research. Most likely, somewhere in the middle (3 to 6 years). I'm afraid to say that's not much time.
Reserves from shale oil, the tar sands and the Orinoco heavy oil & tar from Venezuela are usually what's cited by those who are Pollyannish regarding the future. None of these sources will make a significant contribution by 2015 and likely beyond. This is a large part of the problem with reserves accounting. It is also a problem for all of us.
best --
Dang you beat me :)
Thankyou for that. It is easy to loose sight of the important sometimes. A billion barrels here, a billion there
Nice simple analysis but the next big question is how much of this remaining oil is easy to produce.
How much is in large fields ?
How much is on land ?
Where is the next Ghawar ?
The answer to these questions is probably it does not exist.
The back slop URR assumes we have not already surveyed a good percentage of the earth looking for oil. I think if its possible to consider how much of the remaining oil is probably in known reserve regions you will find that very little exists outside our known deposits.
So analysis of the backside of peak oil is far more complex then determining the front-side production rates to peak.
So the basic question post peak is what is the distribution of this remaining oil ?
To take the US as and example we could calculate the percentages of oil present in various fields and expand that. The answer is of course known, within say 10 years post peak most of the remaining oil is in small or hard to produce fields. This means that for a oil driven economy like we have today we probably will only produce say another 500 billion barrels of oil before it becomes uneconomic to maintain our current oil based infrastructure.
At 30 billion barrels a year this gives about 16 years of reasonable post peak production rates.
The reason this is important is the public if they are exposed to discussion of peak oil here numbers like 2-3 trillion barrels of oil remaining and it results in a false sense of security. A sound and reasonable analysis of post peak production is important to give people and understanding of how little time we really have to use the remaining reserves to smoothly transition our economies.
Discussion of remaining URR without considering its distribution/producibility is not that helpful. We can and should determine the "real" URR for sustaining our economy.
USA was very well endowed with oil. Far greater than the world average, I'm sure.
It would be great to find a simple way to do the statistics, but alas, I think the hard work must continue...
But its averaged against the ME for example.
I think its pretty sound the US has enough of a range
of geologic features to consider it as a model.
I just think that discussion of remaining URR is misleading
since the nature of the reserves change.
I just finished reading 3 articles with discussions with the major western oil companies. They discount peak oil but then tout their expertise in extracting oil from difficult and depleted fields. It does not take a genius to see the problem with this.
There basically waiting right now for government owned companies to cry for help in producing there oil resources once they go into depletion. They know that most of the government owned oil companies don't have the technical ability to keep production up when the easy oil is gone.
I think most of the western oil majors expect to make a lot of money over the next few years as the goverment controlled oil companies have no choice but to ask for help in producing the remaining oil.
Look at Libya for example its just the tip of the iceberg.
The list of countries that are going to be "invaded" by the western majors is long.
Libya
Iraq
Mexico
Venezuela
Iran
Russia
Saudi Arabia
The point is the Western majors are looking at a bonanza if they can continue to deny peak oil long enough to profit handsomely from the back side of post peak production.
They know that sooner or later all these countries are going to see production start to collapse and only advanced methods are going to slow the decline.
The only places that the majors can expect to be able to develop are the US and Canada. And they are already developing all the fields that they can reasonably expect to develop. My real expectation is that the majors will sell all of their production and just be refiners and marketers in the future. The future in the world is with the independents and the national oil companies.
The Majors know geo politics well.
There back in Libya now who would have though that ten years ago.
The NCO have a problem they have coasted the last 20+ years on the fact that they have large reserves of easily recoverable oil. Outside of KSA/Russia(?) that have not developed the expertise to extract from post peak reserves. The majors have the ability.
Consider Mexico/Pemex. Large debt and most of the money goes to the goverment. Suddenly there faced with falling production
or probably more correctly collapsing production. Now the NCO is in a bad situation pretty much regardless of the price of oil. The goverment has been pumping the oil money into the economy for years to uphold its powers. Suddenly oil revenue begins to drop what are they going to do.
1.) Husband the national resource and rest the fields while they try to increase production via favorable contracts with the majors or satelite western oil firms. And basically admit peak oil.
2.) Give in and invite the majors back in ( Libya )
Now consider the NCO finicial situation.
Production dropping by 10%
Internal demand increasing by 5% (WestTexas ExportLand tm )
This mean they need the price of oil to increase by 15% to stay revenue neutral.
Internally there is the expectation that revenue is increasing as the price of oil goes up lets say the populace of the NCO country feels it should get 5% richer each year.
So there is enourmous pressure to increase revenue by at least 5% to match the rising oil prices.
The only way to do that is to increase production even if a significant amount of the revenue from the new production goes into the pockets of a major oil company.
Of course the majors are going to claim that not only will they offset the decline but they can increase production for the NCO. (doubtful)
So the NCO's and associated goverments will be in a pretty tough situation. Either they try and keep production going with the expertise they have in house and see revenue begin to drop say at 5-10% a year or more as rising oil prices fail to cover the lost production or they cut a deal.
Think about it the NCO will be in the situation that they really want oil prices to rise at 20% a year so they can show revenue increases.
60->72->86->103
Unless I'm wrong this is a very very important point.
Peak Oil is also basically peak revenue for the oil producers. They will never make as much money post peak as they made at the peak.
Of course the price will bounce around but you see the trend.
Now lets consider the actions of the big players in the Oil industry.
1.) The Majors are not intrested in peak oil in fact they generally aggresively deny it. Why ?
They know a big payday is comming as they reenter former NCO countries and develop the tired fields to "increase" production.
2.) Opec is acting very strange even with the high prices. Why ? They need the price of oil to continue to increase at a nice rate just to break even as they deplete. Right now Opec or better KSA needs a 20% yearly increase in oil price minimum to offset dropping production. If there depletion rates are higher then 10% the problem is simply worse.
In the real world the price will almost certainly begin to fluctuate over a wide margin as demand destruction internal revenue needs and depletion play out so expect the situation for the NCO to be fairly grim as there revenue begins to fluctuate fairly wildly.
Over the past few years we have seen the big run-up in prices as we have peaked and lost all reserve production. This has resulted in a large cash infusion into the NCO countries the problem is that post peak they won't see any more hefty increases in revenue as demand destruction dampens the price and simple depletion/internal usage cuts into the amount of product they have to sell regardless of price.
The winners here are the majors everyone else loses.
They only monkey wrench is how many deal will go to the Chinese.
Mark my words, in ten years you will see the majors mostly out of production of oil because they can't make any money at the game. All it does is draw flack from environmentalists and from people enraged at ",windfall profits" , and they will see that they will be much better off as refiner/marketers such as Valero. So when flush production collapses you will see them dump the fields, shit on all their E&P employees and tell the touts on Wallstreet that they don't have to worry about decining reserve base because they don't have reserves. And I'll sign my name to that prediction.
Bob Ebersole
I don't disagree with most of what your saying.
I'm just saying that they expect the NCO to invite them back to produce the old and difficult fields.
Tell me what you think the NCO's will do in the scenrio I've outlined.
Oil price increases 10%
Production declines 10%
Internal usage increases 5%.
The are making less money every year and they don't have the expertise to extract the older fields like the majors do.
In exchange the majors get to book reserves in these countries.
Give me your opinion of how the NCO will operate refute my claim that they will be at best revenue neutral post peak for example. You have not addressed my prime example Libya.
So please give me your position on the NCO's not just the Majors.
Now once this scenario plays out I agree there is a saying that goes like no icebox company ever manufactured refrigerators. The oil majors will not be players in alternative energy. But because I see that the NCO's will get desperate I think your missing a step.
Mike
Exxon and Chevron can't make money on 9 barrel a day wells,the median production in Texas, and they won't. They'll lay off the exploraationists and retire the production engineers, and the NOCs and service companies will hire them. This is what they did onshore in Texas and Louisiana, they will do it again because they will come to percieve that that will make more money. And they will be too controversial to get NOC contracts.
As for Libia, I'm pretty sure that it was the treat of invasion that made Gadafi come to Jesus. The international oil companies were already buying their products for use in Europe. American companies ignore US sanctions at will as they suffer no penalties.
KSA can pull off hiring the small companies as contractors since they have the infrastructure for building big project.
I think that the rework project needed to try to keep production rates up will be large and complex. I don't see most NOC capable of pulling them off. You have to consider that when depletion finally sets in most of them will be hit by surpise. I'm sure Pemex even with the warning that we know that have been given is not seriously working on how to keep the oil flow up if Cantrell tanks. I suspect that many of the NOC's are more delusional then Pemex about their production capabilities.
I think your underestimating the pressure that the NOC will be under to keep or even increase their oil revenue.
I'm not convinced that simply taking the approach of business as usual and hiring in foreign contractors is going to solve the problems there facing.
Now I do believe the major's are capable of keeping production rates up in depleted fields at the expense of total recovery and with steeper declines later in production.
Now if they don't bring in the majors the NOC's could very well be facing production declines steep then 10% if the situation in the fields gets beyond their ability to handle with contractors. Realize that after the US peaked the drilling campaign was massive and probably won't be repeated even in the situation I'm talking about.
I suspect we will soon find out.
If I'm right then I'd expect the initial drops in production rates to be fairly gentle with declines say in the 2-5% range but say going rapidly to the double digits 10-20% several years later. Consider if they try to put together a number of contractors for a large project they will be faced with a lot of issues. The contractors will be unwilling to sign long term deals since the price the can charge will be skyrocketing. I can foresee numerous delays and problem as contracts pressure for higher prices or leave for greener pastures. The reason I think the major can pull it off is they will have the backing of the western governments to ensure that the projects are kept on schedule. Politics will play a big role in ensuring the success of NOC projects that accept the help of the majors.
If your right then we will probably see initial declines say in the 5-10% range moving fairly quickly higher.
I do see in this case that internal political issues could become explosive. So I'm not convinced.
==M.
One might also consider the African continent, the largest after Asia. There are decent deposits in North Africa, and around the Niger delta, but most of the continent is virtually bereft of oil.
A small number of locations around the globe have most of the oil. This is also true of a number of other resources, such as copper, gold and diamonds.
The concept above is vaguely interesting, but I'm afraid it doesn't have much merit.
I think the approach posted of extrapolating the US peak only to regions that have oil makes sense.
And the current approach is valid what it gives is a upper bound on the amount of oil available. Its simple and you can assert with almost a 99% certainty that there is less then 2 trillion barrels of oil remaining. So yes it has merit and is valid as long as you recognize that its probably a good upper bound.
The next upper bound is I believe the approach of extrapolating the US peak to oil producing regions.
Next you get into detailed arguments.
I think that once you consider all the factors we will recover at best another 500 billion barrels of oil period.
Which gives 16 years at our current usage or probably 20-30
in reality.
Once you can no longer support growth in a oil based economy it will rapidly shift to a new economic model or more likely adopt some of the the past models. In general it looks like the new economy will be one based on concentration of wealth and power not generation of new wealth if you can call this new.
The only real difference this time around is that we will have high tech kings. The consumer industry will probably shrink but I think electronics will stay popular since you need to give the masses their circus.
1.) Health Care ( probably continue to advance but subsidized to focus on the health needs of the wealthy.)
2.) Electronics consumer goods continue (Circus needed)
3.) Communications continue to grow ( Post peak they will be even more important)
4.) Military technology ( Massive growth )
5.) Alternative energy
6.) Electric rail transport for the masses and advanced air transport for the wealthy.
As you notice these are all industries that have a low footprint most are "Cyberspace" focused or biological. I don't see any growth in the traditional manufacturing/consumer goods. Its funny that it looks like in the end a small number of people will get their flying cars. For the general population I see a massive move back to agriculture but I'd not call that growth followed by re-industrialization in the western countries to support basic needs ( Kitchen goods, bicycles, clothes,cheap toys etc) this is not growth. Recycling the McMansions will probably be a big industry for a while.
The wealthy get besides the traditional trappings of wealth.
Huge homes servants (slaves)
Advanced health care,Flying cars,Instant advanced unrestricted communication.
The poor get Xboxes and Cable TV and restricted internet access along with either a long rail commute or a small flat in the city. I suspect in a lot of the world poor people will be sterilized probably via sterilization drugs after one child if they are lucky. They will get enough health care to prevent massive plagues along with basic medicine.
Sterilization will be used to punish most breaches of law.
The military gets many cool new toys to keep the status quo.
The middle class will be reduced to the technical and managerial people needed to support the rich, military and oversee the masses.
And we probably will sit here for years until we have two technical breakthroughs
1.) Fusion
2.) A real space elevator or cheap space access method.
And the world population drops back to a reasonable levels.
http://en.wikipedia.org/wiki/Tethys_Ocean
It would be interesting to know how much of the bed of Tethys has not been explored.
Heaven forbid.
The MMS estimates that the quantity of undiscovered technically recoverable resources ranges from 66.6 to 115.3 billion barrels of oil and 326.4 to 565.9 trillion cubic feet of natural gas. The mean or average estimate is 85.9 billion barrels of oil and 419.9 trillion cubic feet of natural gas. These volumes of UTRR for the OCS represent about 60 percent of the total oil and 40 percent of the total natural gas estimated to be contained in undiscovered fields in the United States. The mean estimates for both oil and gas increased about 15 percent compared to the 2001 assessment. For the oil resources, the vast majority of this increase occurred in the deepwater areas of the Gulf of Mexico, while for gas resources the majority of the increase was in deep gas plays located beneath the shallow water shelf of the Gulf of Mexico.
These estimates represent the potential quantities of undiscovered hydrocarbons that can be conventionally produced using existing or reasonably foreseeable technology, without any consideration of economic feasibility." MMS Outer Continental Shelf Oil and Gas Assessment 2006
Not a single mention of the word "hurricane" in the assessment though.
This has a couple of major effects on exploration and exploitation. Although we were not the first area s to discover oil (Roumania and Baku were first), we wer the first to develop modern useage as fuel. Individual wildcatters found our first and greatest fields, and some of the companies they founded became the International Oil Companies. Exxon, Chevron, Texaco, Gulf, Sun, Amoco and many more were started this way.
The US is not a democracy, but rather a corporatocracy, and the courts upheld contracts with corporations even at unfair profits and terms. Overseas, national governments responded to unfair contracts and practices by confiscating the production, and now about 80% of the world production is owned by national oil companies and closed to US corporations, and the percentage is growing.
Major oil companies and national oil companies cannot profitably exploit small oil fields or fields with low production rates. They just have too much overhead. Office towers full of accountants, public relations flaks and micropalentologists cost a lot to support, I doubt Exxon breaks even on a well producing less than 50 barrels a day. So there is a space for independents and professionals to enter the oil patch and make money on smaller scale prospects. This is great, its how WestTexas and I both make our livings.
The upshot is that the United States is much more mature than most of the world will ever become. Yes, I know that most of the world's production comes from supergiants fields and always will. But I'd bet that 30% of the fields in the US would never have been developed by the majors any time in the last 60 years.
So, estimating world recovery by using US data is fallacious. Major oil companies are neither efficent oil finders or producers, compared to individuals If you'd like I could give you examples ad infinitum.
There are two crescents of oil rich lands on the planet. One starts in Alaska, passes south through Texas and Mexico then swings east into Colombia and Venezuela. The other starts in N. Africa, swings west through the Persian Gulf and up into the various `Stans, then onward north into the Urals and Russia.
It seems to me that the USA encompasses a fairly large swath of these oil rich lands, so to generalize from the experience of this country is to arrive at too high an overall figure. If you performed the same exercise with China you would get a lower figure for the world, or so it seems to me.
Along these same lines, I've sometimes wondered about a slightly different question: how much oil would have been extracted within the continental United States IF IT WERE THE CASE that the only oil on the planet were found within the USA?
The question has relevance because at planetary peak there will be no low cost oil coming from somewhere else.
The answer I come with is this: if the only oil on the planet were the endowment of the USA, then LESS oil would have been produced in the USA in the years since 1970, compared to what in fact was produced.
This seems counter-intuitive (assuming it to be correct) because the price of oil in the hypothetical USA would have been much higher than was actually the case. So why would not more of oil have been extracted?
The answer hinges on the question of marginal cost? Yes, higher priced oil means more oil is extracted. But higher marginal cost oil means less is extracted.
Another way to say the same thing: think how much food has to be given up to get the next barrel of oil. In the actual USA since 1970, the food cost of oil has been low, because cheap oil from abroad has meant cheap and abundant food at home. In the hypothetical USA, the food cost of oil would have been high, because oil would have been expensive, hence food would have been expensive and less abundant, hence there would have been less food around to give up in exchange for oil, hence we would stop giving up food for oil sooner compared to what actually happened. (And I am saying, obviously, that what happens with food happens with everything.)
If this line of thinking is valid implications for the world post-peak seem quite sobering.
As is usually trivially accepted, when the price of oil increases, more reserves appear economically accessible.
However, the corollary is rarely acknowledged. A decreasing price (via global recession) or increasing costs (as you discuss) can mean booked reserves are no longer economically accessible.
Too many people imagine genuine booked reserves to be a floor for URR. This is not a logically necessary condition.
That's how you calculate oil potential before you drill and find out if there is actually any source rock there to produce oil to be trapped.
2. How much of the world's road net does the US have?
That's how you calculate how much of the world's small oil fields are accessible to drilling. No one is going to drill a million barrel oil field if he has to build a hundred mile long road to get there and to get the oil out. Well, at a price lower than we can make methanol from coal, anyway.
FromAn Open Letter to the Energy Modelling Community: (Article by Bentley, starts p.6)
Continues at http://www.iaee.org/documents/06spr.pdf
One of the problems of any set of pointy headed geeks is presenting evidence to the average person in a non-boring, understandable fashion. I see that as the big strength of yor new method for calculating reserves. But, as I and several other posters have noted, this may be too high. I guess 20-20 hindsight will clear everything up, if I can just live long enough to gain a historical perspective, therefore onward through the fog!
gtjeffers, you're right, I didn't subtract the US surface area. That recomputes the projected world URR to 2.53 trillion barrels.
I also understand the comment about using a region such as Australia to get a lower number. My assumption was that the USA was broadly more representative of oil field distribution worldwide. Australia is not. The USA may actually prove to be over-endowed by virtue of natural deposits and being the most accessible of all regions. The question would arise as to what is a "typical" oil endowed country. I don't know as it depends tautologically on world URR.
Still, interesting that the numbers came out close to the expected range.
If one wishes to avoid using projected URRs and only use hard numbers, one could use the amount of oil produced at the time of US peak and scale that up to what the peak may be for the world. Since the US peaked at 109Gb, that scales up to 1.41 trillion barrels for the world.
Just a bit of interesting number juggling.
Thats probably a closer answer but still too high.
I think its easy enough to consider the world to be composed of basically two oil belts as mentioned earlier.
The north American belt from Alaska down through Venezuela and the Asian one from north Africa through western Siberia.
The rest of the regions would be combined china north sea etc.
So if you discount the inflated prediction from land that is non sedimentary then its probably lower then this say
1 trillion barrels.
I think your approach to get 1.4 is closer to a real number but you should only consider known large oil producing regions not the whole world.
I've argued that real oil recovery i.e oil recoverable at a cheap enough price and high enough rate to support a oil based economy is far less then the URR.
Consider the US economy if it had just grown within the constraints of oil found within its borders this is what will happen post peak for the world. I doubt the GOM would have been extensively developed in that case.
I'm a big fan of Harry Turtledove who writes alternate histories it would be cool to see him do one on the US under such a constraint. The cause could be say recognition of oil as a national resource and refusal to sell on the open market ( So we don't end up like the US)
Considering I was too young to really understand the Moon missions for me its interesting that it looks like I'll actually live through the two biggest events to happen to mankind peak oil and global warming.
No one on the "cornicopian" side of this argument has any vision of growth really diminishing, flattenting out, or just plain peaking within any sort of short time frame. But even at at nominal 2% growth rate, in a mere 34.69 years, the oil consumption rate MUST be 170 MBPD. Any number less than that means that 2% annual growth is not "likely" from the cornicopian view. That's the math that is undeniable.
Furthermore, it also means that in the ensuing 34.69 years (at 2% annual growth) more oil will be consumed than has been consumed over the entire history prior to that. That is another part of the math that cannot be denied.
That's the nature of exponential growth and it also means that you blow through what ever flowable, recoverable reserves that do exist at a rate much faster than the linear (at today's rate) suggests.
Add to that the declining production rates of fields past their peak (reserve growth may extend time to shutdown but is unlikely to reverse the long-term decline) and you have to be able to tap into the "reserve" at even higher rates to offset the losses.
It's hard for many to think in non-linear terms(exponential growth and declines). This, however, is one of the things it takes to wrap one's mind around this issue.
The world has an abundant supply of oil, and high petrol prices are just the reality of a globally-traded commodity, ExxonMobil Australia chairman Mark Nolan says.
Mr Nolan used his speech to the Asia Pacific oil and gas conference in Adelaide on Monday to debunk the theory of peak oil, which suggests oil supplies have peaked and will dwindle over the next 20 years.
"The fact is that the world has an abundance of oil and there is little question, scientifically, that abundant energy resources exist," Mr Nolan said.
"According to the US Geological Survey, the earth currently has more than three trillion barrels of conventional, recoverable oil resources.
"So far we have produced one trillion."
So where is the production?
Am i to beleive that it's safe to buy a Hummer now?
First, the USA does not have "average geology". I'm not 100% certain of my facts here, but I believe that crysatline cratonic areas (think Canadian Shield) are under represented in the USA - and these areas would normally not have any oil. The USA also has many and diverse sedimentary basins - that do have oil. So I would suggest that USA geology is heavily skewed towards having oil and gas and this approach will over estimate the world.
US geology map here:
http://geology.about.com/library/bl/maps/n_map_usa48geo.htm
Second, a point you touched on yourself, much of the global oil resource lies off shore on the continental shelf - which is essentailly a submerged part of the continent. So it is not the area of the continent but that of the continent + continental shelf that you need.
Think Norway - zero oil on shore - but a fair bit of oil off shore. You get a picture of the World's tectonic plates here:
http://en.wikipedia.org/wiki/Plate_tectonics#Key_principles
but it's not the plate areas that you need - it is the contintal shelf area - and I'm not going to try and find this.
If you wanted to take this a stage further then you should do it for the N American continent - US, Canada, Alaska and Mexico (plus Greenland?) - land + shelf. That way I think you get something more representative of the worlds average geology.
My thinking on offshore was that since the US coastline to surface area ratio was comparable to the world's and since most companies drill at roughly the same distance from land worldwide, then things would just cancel out when you divide the numbers.
The geological distribution of oil was more heterogenous than I thought. I am not sure how valid it is to only scale up to all oil producing regions. After all, not all states of the US are oil producing which reflects on a global level the fact that not all countries produce oil either?
Maybe I'll take Khebab's advise and recalculate on a smaller land area.
My gut feeling is that nothing will eventuate.
I wonder if your estimate could be refined by considering only the red areas above (note that they excluded the US from their study).
Bush is on to this new-fangled theory.
It can only mean one thing.
Mars, bitches!
And then, Jupiter and Saturn.