A new study says that there's petrol, diesel and even electricity - but soybean could be fuel of the future.
Vanadium nitrogenase, an enzyme found in the roots of soybeans, produces ammonia from nitrogen gas.
But it can also convert carbon monoxide (CO), a common industrial by-product, into propane, the blue-flamed gas found on stoves across America.
Markus Ribbe and his colleagues at the University of California, Irvine, isolated this enzyme to convert nitrogen into ammonia.
Then they removed the nitrogen and oxygen and filled the remaining space with CO.
As a result, the enzyme began converting CO into a carbon structure that resembles propane, the blue-flamed gas used in kitchens across America.
"Obviously this could lead to new ways to create synthetic liquid fuels if we can make longer carbon-carbon chains," Discovery News quoted Ribbe as saying.
If perfected, the technique could lead to cars partially powered on their own fumes. Even further into the future, vehicles could even draw fuel from the air itself.
One hitch is that the extraction of the enzyme is very difficult. So further studies are required to perfect this technology.
The study appears in the journal Science.