Just like anything in economics, if the price of a commodity gets too expensive, it's alternatives/substitutes become more attractive. Add in economies of scale and technological tweaking and you reach a fundamental shift.
Here's one possible direction: biodiesel from algae and 'pond scum' --
http://www.businessweek.com/globalbi...tm?chan=search
It's not ready for primetime yet but there's quite a bit of venture capital going into it. Similar to the bacteria-based hydrocarbon farming I posted about earlier.