Although the technology looks promising, "the whole industry has been haunted by hype," says Leonard Wagner, an analyst at London-based Mora Associates

and author of a 2007 report on the algae biofuel industry. Wagner estimates that it will be four to five years before any company goes commercial with the technology, and a decade before anyone produces a meaningful amount of biofuel using it.

In order to be cost competitive with petroleum, the price of algae biofuel will have to be $50 a barrel, says Wagner. With today's technology, algae biofuel could be produced for around $400 to $1,600 per barrel, says Al Darzins, group manager of bioenergy at the National Renewable Energy Laboratory, in Golden, CO. Darzins says that in order to make the economics work, companies will have to sell more than just the biofuel. For instance, algae oil could be sold as cooking oil, and the biomass, which is rich in protein, could be used as animal feed.

Another idea, says Eckelberry, is to locate algae plants next to power plants or other major emitters of carbon dioxide. Carbon dioxide could then be sequestered and fed to the algae, which need it to grow. Particularly if a price is put on carbon emissions, this could prove to be a good scheme, says Eckelberry.