It sounds too good to be true. Take some fallow land that is unsuited for growing food. Build some ponds and let microscopic algae bloom. Harvest the algae, extract the vegetable oil and turn it into a green-tinged transportation fuel.

The truth is, it is too good to be true -- at least right now. While engineers can grow small batches of algae in beakers in laboratories and convert it into fuel, re-creating that process on an industrial scale has proved elusive and expensive when compared with the price of gasoline.

Still,...