Well, in a few hundred years, if then, alternatives will have been found. On the other hand, The Russians determined over a century ago, that most oil is NOT composed of ancient plants and dinosaur bodies. The depths of extraction now are far below the levels of the prehistoric jungles. Chemical analysis also concurs with that, as does the Second Law of Thermodynamics. That is one reason that so many estimates of available resources in existing wells doesn't fall nearly as fast as "expected". The reserves are being replenished from below. The Russians refer to it as "juvenile planet fluid"; that is, a component of the original creation of the planet trapped deep in the mantle, being forced out by tectonic pressures. There are no estimates of the possible reserves, the question is how to get to them since the replenishment pathways move with the plates. As an aside, so do geothermal resources. The Supercaldera under Yellowstone has moved from the Montana/Dakota boundary area to it's present location in Wyoming by that action. We are extracting fluid oil faster than can be replenished in many areas, fracking for oil as well as gas is an option in some areas. But we have more than enough energy resources for centuries IF WE JUST DEVELOP them! Use gen 4 or 5 nuclear for electric, gas for peaking. Supercritical new gen coal in areas too close to seismic areas. We have the technology now, eventually we may even have fusion. What we need is to get the government out of the way!