Small change...
Consider the Green River Formation:
The Green River Formation--an assemblage of over 1,000 feet of sedimentary rocks that lie beneath parts of Colorado, Utah, and Wyoming--contains the world's largest deposits of oil shale,Anu K. Mittal, the GAOs director of natural resources and environment said in written testimony submitted to the House Science Subcommittee on Energy and Environment.
USGS estimates that the Green River Formation contains about 3 trillion barrels of oil, and about half of this may be recoverable, depending on available technology and economic conditions, Mittal testified.
The Rand Corporation, a nonprofit research organization, estimates that 30 to 60 percent of the oil shale in the Green River Formation can be recovered, Mittal told the subcommittee. At the midpoint of this estimate, almost half of the 3 trillion barrels of oil would be recoverable. This is an amount about equal to the entire world's proven oil reserves."
Not only that, but look how far we’ve come in drilling technology since the Drake well in 1859. What will the next 50, 100 or 150 years bring? What isn’t recoverable today surely will be soon enough. It ain’t going anywhere.