Officially, Venezuela has the world’s largest crude oil reserves with 303 billion barrels of proved reserves. But, a lot of this oil is extra-heavy crude oil, and may not be economical to produce at prevailing prices. Thus, some portion of Venezuela’s barrels may in reality no longer be in the “proved reserves” category.

Consider that Venezuela’s proved reserves jumped from 80 billion barrels in 2005 to 300 billion barrels in 2014. The main reason for that wasn’t a bunch of new oil discoveries. No, it was the fact that oil prices had reached triple digits, making Venezuela’s extra-heavy oil economical to produce. In other words, “resources” (the oil in the ground) were moved into the “proved reserves” (oil that is economical to produce) category.

Saudi Arabia, on the other hand, reported 264 billion barrels of proved reserves in 2005, and 267 billion barrels in 2014. Saudi Arabia’s barrels were deemed to be economical to produce even before oil prices spiked. For that reason, I consider Saudi Arabia’s proved reserves — 16% of the global total — to be of the most significance to the global oil market.

But doubts about the amount of Saudi Arabia’s reserves have persisted for years. In 1982, Saudi Arabia stopped allowing their oil and gas data to be scrutinized. Prior to that, outsiders had some access to information on their reserves. When that accessibility was shut down, Saudi proved oil reserves were estimated to be 166 billion barrels.

However, around 1988 Saudi raised their estimate of proved reserves by 90 billion barrels. Many pundits have suggested that this upward revision was based on internal OPEC politics. Since the reserves were no longer subject to outside audit, there was a great deal of skepticism around the official numbers the Saudis released.

The skepticism deepened when one considered that Saudi’s reserves in 1990 were 260 billion barrels, and today — nearly 30 years later — they are reportedly 266 billion barrels. Meanwhile, Saudi Arabia produced over 100 billion barrels between 1990 and 2017. How then could their reserves be essentially unchanged?

In preparation for a potential IPO, Saudi’s national oil company, Saudi Aramco, commissioned an outside audit of its proved reserves. The external audit found Saudi’s proved oil reserves to be at least 270 billion barrels.

But doubts persist. For example, oil economist Dr. Mamdouh G. Salameh, who is a Visiting Professor of Energy Economics at ESCP Europe Business School, London, recently wrote:

My calculation of Saudi reserves based on Saudi production since the discovery of oil in 1938 till now (for which we have figures) and a deduction of an annual depletion rate of Saudi aging fields averaging 5%-7% for the same period, gives a figure of 70-74 bb of remaining reserves. My figures are more or less in line with those of other experts.”

I once did a similar calculation. I started with the assumption that the 1982 estimate of 166 billion barrels was correct, and then I just subtracted Saudi production since then. I calculated their total production since 1982 as ~100 billion barrels, leaving 66 billion barrels of reserves.

However, I then did a sanity check that threw that calculation in doubt. I did the same calculation for the U.S. proved reserves over the same time frame.

In 1982, U.S. proved crude oil reserves were reported to be 35 billion barrels. By 2005 — and before the shale oil boom was underway, U.S. proved reserves had only fallen to 30 billion barrels. But total U.S. production between 1982 and 2005 was 77 billion barrels.

If we extend that calculation through the end of 2017, U.S. proved reserves have actually jumped to 50 billion barrels (per the 2018 BP Statistical Review), and there have been 117 billion barrels of U.S. production since 1982.

To reiterate, in 1982 U.S. proved crude oil reserves stood at 35 billion barrels. Between then and 2017, the U.S. produced 117 billion barrels of oil, yet proved reserves grew to 50 billion barrels.

How did this happen? There were new discoveries, technological improvements that allowed more barrels to be extracted from existing fields, and higher prices that made additional resources economical to extract.

I think it’s reasonable to assume that Saudi Arabia also found additional barrels since 1982. They also have access to the same kinds of technology that improved recovery in U.S. fields. Therefore, I do not believe it’s a legitimate exercise to consider depletion from a historical reserves number to estimate current reserves. Such an exercise would have suggested that U.S. oil production would have fallen to zero by 1991.

Thus, I don’t find a reasonable basis for concluding that Saudi Arabia’s reserves are much lower than their official numbers. Their published reserves are consistent with the independent audit, and they are consistent with the experience in the U.S. of reserves growth despite significant oil production.

Lest you think that the U.S. results are atypical, you can repeat this exercise for any of the world’s major oil producers and find the same thing. Starting with the proved reserves in 1982 and subtracting the subsequent production will not accurately predict the reserves at some point in the future. In many cases — as with the U.S. — cumulative production was greater than the 1982 proved reserves number.

So, I have thus far found no good reason to doubt Saudi Arabia’s official numbers.

This article was originally posted at Forbes, and prompted some emotional reactions from some readers. Often, it was clear the person responding hadn’t actually read the article. In a follow-up, I will address some of those comments.