Plus, wasn't the 1975 figure of 60 GB in reserves for Ghawar based on the excessively conservative P-90 SEC reporting rules-type estimates by US majors, rather than the P-50 estimate that is more reasonable for the kinds of purposes pursued by Stuart?  And as such, isn't JD debunking Simmons based on a red herring in the link you reference?
When I see Simmons' slide, I see him raising questions about the durability of Ghawar production. I don't think he's claiming that its URR is exactly 60, but I do think he's making the point that it is far from infinite, which is what some seem to have believed until Simmons started challenging common lore about KSA oil. I think he should make this clearer in his presentation, because JD makes a good point. However, what is the point? How much does JD think is really there? Even if there was 90 GB we have a problem. The big problem, as noted by everyone here, is no transparency, no way to validate the numbers whatever they are. I also think there's lots of reason to believe that Ghawar has actually peaked, which is the only important point here.
However, what is the point? How much does JD think is really there?

How would I know? I don't even really care. The basis of my optimism isn't that there's lots of oil left, although there probably is. The basis of my optimism is that we, humanity, don't need oil.

I also think there's lots of reason to believe that Ghawar has actually peaked, which is the only important point here.

I strongly disagree. You're basically saying "There's lots of reasons to think the poppy fields may be in trouble, which is the only important point here."

The status of the poppy fields may SEEM to be the only important point to the heroin addict, but it's not actually. The only important point is the fact that the person is addicted to heroin. That's the real root of the problem. The poppy fields are just a red herring -- a focus of junky denial which ignores the real problem.

Fascinating response! I'm interested in your views about being addicted to oil and that we don't need it.

When I said "the only important point," I didn't mean overall, just in terms of the specific discussion of Ghawar reserves. I didn't think the number of 60 vs 90 vs whatever was that important if the field's production was peaking (which I know is under debate - I've just expressed my intepretation of the data I have seen). Its production is what matters, not the number. Certainly it's not the most important issue in the issue of oil dependence.

BTW, I have to agree that circumstances have prevented validation or refutation of the USGS projections. I disagree that their analysis has been substantiated, but agree that we don't know how right or wrong they are about Iraq, Greenland, etc. I do know that as long as the oil remains undiscovered for whatever reason that it won't help against the peak oil concerns.