Get ready to feel a little less guilty about the carbon footprint of your air travel — at least if you're flying from Los Angeles to San Francisco on United. The airline will be using fuel made from beef tallow (fat) for the 378-mile flight between California cities. NPR reports It has purchased 15 million gallons of the biofuel.

The purchase is part of United's Eco-Skies commitment to the environment. In addition to purchasing biofuel to use in it jets, the airline has invested $30 million in the company Fulcrum BioEnergy, which "uses household garbage, including food waste, for its fuel feedstock."

United isn't the only airline adopting more environmentally friendly fuel sources. FedEx and Southwest Airlines have bought fuel from Red Rock Biofuels, which makes jet fuel from forest waste.

crews refuel a United Airlines jet planeCrews refuel a jet plane for a quick turn around on tarmac at LAX Los Angeles airport. (Photo: Meister Photos/Shutterstock)
Tapping into waste for fuel is obviously not anything new, but The New York Times reports that airlines have been slow to use them. Now it looks like that is changing. The fuel is available in large quantities and the price makes it very attractive.

Fulcrum BioEnergy says it can produce biofuel "for a lot less than $1 a gallon." During the first quarter of this year, United bought jet fuel at $2.11 a gallon.

This could be the beginning of a positive environmental change in the airline industry. As long as biofuel makers can continually increase supply (and we certainly create enough waste from foods and other trash to do so) and it will be cost-effective for the airlines, the skies may be a little cleaner.

But this makes me wonder: Will the airlines pass the fuel savings on to consumers?

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.