It was obvious that oil was a finite resource from the start, but it took the better part of 100 years of exploitation for US oil production to peak. Five or ten years doesn't seem long enough to reliably spot a trend on that scale.
I'm surprised Simmons expected such high prices. As the shock in 2008 illustrated, above a certain price, oil users cut back as much as they can, which lowers the price again. A sustained price of 200 2005-era dollars per barrel is a really high; that price would surely kill a lot of demand, which would probably prevent it from being sustained. Eventually, we may see $200/bbl, but it will probably be quite a while.
I know hindsight is 20/20, but still, I would have thought a better bet would be something about the average price of oil over (say) a five year period always being higher than the average price over the previous five year period. Then again, maybe Tierney wouldn't have taken that bet.