Algae doesn't need land to grow. And, importantly, sequesters more CO2 than any other plant in the process. Producing a lot of oxygen as a by product.
There's at least 60,000 different species -- and probably a lot more -- with some microalgae containing up to 50% lipids or vegetable oil.
Importantly, algae also promises no change in infrastructure required.
After all...oil itself is essentially fossilized algae.
Valcent produces algae in their closed loop "bioreactors" -- initial test runs were at 33,000 gallons an acre -- on semi-arid land in Texas that can't be used for food cultivation. To put that in perspective, palm, which I believe is the next highest source, can get some 6,700 gallons an acre.
Valcent thinks it can find the right algae species to get them up to the 100,000 gallon level. Indeed, they claim that if 1/10 of the state of New Mexico were used for algae production, they could meet the energy demands for the entire United States.