>>going to have a diminishing supply, so prices will go up
A friend who is a biologist who does business acquisition in biotech told me several years ago that almost every polymer can be made from biologics. The only issue at this point is cost, but the cost curve is relatively steep since they've only just started optimizing enzymes and such for this. He thought that sooner or later, it would be cheaper to make many plastics and petro-based chemicals without petroleum. As a business strategy, he was looking for the highest margin products because that's the easy place to start. But as your processes get more efficient, you move down the market.
And unlike the petroleum industry, there is the possibility of 100x increases in efficiency.
Now, the caveat there is that despite GW Bush talking about making fuel from cheat grass and corn stalks, we haven't seen any, which suggests that optimizing these enzymes is harder than anyone thought.
But basically, my friend was saying that fuel oil, gasoline and all that are at the absolute bottom of the value chain and that non-petro replacements would start at the top and, he thought, never get to profitability on a broad scale for fuel, and we would have to convert to an electric economy or find other completely different solutions at the bottom of the value chain.