And space. A lot of it.
By comparison, Colorado has 104,185 square miles. Nevada has 110,561. New Mexico has 121,589. Utah has 84,897. Arizona has 113,991 and Texas has 266,833. I mention this because these states have large amounts of arid climates.
You could reasonably take 1,000 square miles from each of six states, turn the desert land into algae farms and replace the oil production for all of the United States.
One problem is the cost to build the vertical algae tubes. It is about $800,000 per acre. With one square mile being 640 acres, the price just to build is $512 M per square mile. One could argue that for $600 Billion (less than TARP) the government could have created it's own oil factory. Selling of the oil on the open market would have cut fuel prices, created a revenue generating enterprise for the government. For the amount contained in the stimulus program, would could have had two such “farms”.
The other two major problems are where to get all of the CO2 required and the amount of power required to run the pumps, drying equipment, presses, etc. The best answer I have see so far would be to put in coal plants to provide electricity and then take the gases from the coal plants and use that as the CO2 supply.