During a 90 day continual production test, algae was being harvested at an average of one gram (dry weight) per liter. This equates to algae bio mass production of 276 tons of algae per acre per year. Achieving the same biomass production rate with an algal species having 50% lipids (oil) content would therefore deliver approximately 33,000 gallons of algae oil per acre per year. …As a comparative, food crop such as soy bean will typically produce some 48 gallons oil per acre per year and palm will produce approximately 630 gallons oil per acre per year. In addition, the Vertigro Bio Reactor System is a closed loop continuous production system that uses little water and may be built on non arable lands.

http://www.scribemedia.org/2007/12/12/algae-biofuel-valcent-vertigro/