Regarding all the "peak oil" Malthusian pessimism in the press these
days, I found a physics professor online who did the math and arrived
at a techno-optimist replacement solution, by my reckoning.

http://www.unh.edu/p2/biodiesel/article_alge.html

Replacing all transportation fuels (switching everything to diesel,
using algae grown in the U.S.) would not displace food crop or grazing
acreage, could be done in 12.5% of land in the Sonora desert alone
(but of course should be split up and located at various U.S. sites),
and would cost a total of $46.2 billion per year compared to the $100
to $150 billion per year just for foreign oil imports (at mid-2004
prices!). Not quite the end of the world.

Kent