In the U.S., there isn't a lot of enthusiasm for automotive biofuels these days. Concerns over the potential impact on food supplies, the growing sales of practical electric cars, and other factors seem to be keeping most biofuels out of the mainstream.
Yet the use of biofuel in aircraft may be really starting to take off (pardon the pun).
Southwest Airlines is the latest carrier to experiment with renewable jet fuel. It recently signed an agreement with Red Rock Biofuels to purchase low-carbon fuel made from forest residue, according to Green Car Congress.
Southwest will buy approximately 3 million gallons of the renewable fuel per year, with the first deliveries expected in 2016 for use in the San Francisco Bay Area.
The jet fuel starts out as woody biomass feedstock, which undergoes gasification to release a "synthesis gas," which is then processed and liquified into hydrocarbons.
Boeing 787 Dreamliner
This is just one of several ongoing efforts to clean up the skies with biofuels.
KLM Royal Dutch Airlines started using biofuel on flights between New York and Amsterdam last year, while South African Airlines and Boeing plan to test a tobacco-based fuel grown in the airline's home country.
In addition, Boeing is also involved in the development of "green diesel," which is made by splitting molecules from waste oil and fats with hydrogen.
All of these efforts could help lower the airline industry's overall carbon emissions, which account for 2 percent of the global today.
By some projections, that total could rise to 5 percent by 2050.