Biofuels for highway trucks and automobiles have been getting a lot of press, but many people are unaware that airlines have also been investigating alternative fuels. That's no surprise when you consider that the price of jet fuel often determines whether an airline is profitable or not.

One of the leaders in alternative aircraft fuels is KLM, which made the first commercial biofuel flight in June 2011. One year later, the Dutch airline made what it says is the longest biofuel flight ever, when a KLM Boeing 777-200 added fuel made from used cooking oil to some of its tanks and flew from Amsterdam to the U.N. Conference for Sustainable Development in Rio de Janeiro, Brazil. The fuel meets the same technical specifications as traditional petroleum-based material, and no adjustments were made to the aircraft or its engines, the company said.

Azul Brazilian Airlines, that country's third-largest air carrier, recently launched its own biofuel-powered aircraft. In mid-June, the company made a demonstration flight with an Embraer E195 jet powered by fuel produced from Brazilian sugar cane.

The fuel, produced by Amyris Inc., is made by using modified microorganisms that convert sugar into a renewable hydrocarbon. GE provided the jet engine and tested it for compliance with technical and safety standards. According to one analysis, the sugar-based fuel could reduce greenhouse gas emissions by up to 82 percent compared with conventional jet fuel.