...fungus???

I remember on tomorrow's world years ago a diesel engine that ran on algae. The algae grew in a transparent tube that let in sunlight. This plus the CO2 and water from the exhaust allowed it to grow and move up the tube. The heat from the engine dried the algae and as each algae was the size of a diesel fuel droplet, the engine ran beautifully. A solar powered diesel plant engine.

but the big oil producers would never make any money and the government would lose a lot of tax from something so sustainable so it'll be quietly pushed to one side, or bought and shelved