I vaguely remember one group speculating around 800 years a while back. I realized that was probably a bit overblown but still it shined some light on the grift being played on us.
With regards to "oil reserve potentials," I can recall many years back of projections being low in numbers for number of years of reserves. However, I learned that as the oil industry gained more profit, better ways were found to find new sources. So, as long as that continues, I suspect that 200 years is another of those suspicious numbers.