Algae fuel makes little sense. To grow enough algae for fuel usage, you would have to use a lot of fertilizer. The fertilizer would be made from natural gas. So

Algae fuel makes little sense. To grow enough algae for fuel usage, you would have to use a lot of fertilizer. The fertilizer would be made from natural gas. So it would just be a giant scheme of hiding natural gas usage behind green fuel, but worse since it would take more natural gas than just using it directly.