Like [link|http://www.unh.edu/p2/biodiesel/article_alge.html|biodiesel]. Though there seems to be some disagreement on feasibility. While that article is optimistic [link|http://www.fuelandfiber.com/Athena/biodiesel_from_algae_es.pdf|this] claims that prices would have to be 2-3 times the current level for biodiesel to be feasible. (But I'd bet that if biodiesel came into wide use, we'd figure out ways to make it cheaper to produce.)
Cheers,
Ben