Thanks, I always wondered about the mechanics of how that worked. Corollary question: If humans could somehow abandon petroleum and turn to alternate energy sources that were just as efficient (I know, not likely), what would happen over time as petroleum built up gradually over decades and centuries and not be drilled for? Would it begin to pond on the surface? Leach into oceans? I figure that the abiotic production of petroleum never reaches homeostasis and balances out, but just keeps producing.