The first airplanes in U.S. commercial aviation to use biofuels took off this week from Houston. United Airlines Continental flight 1403 flew from Houston to Chicago powered by the first 100 percent algae-derived jet fuel. Alaska Airlines will also fly two flights from Seattle to Washington and Portland powered by a blend of biofuel made from cooking oil on Wednesday.

Biofuels for aviation are derived from a plant sources like jatropha, algae and other waste oils to produce jet fuel. Biofuels are considered one way for the aviation industry to reduce its carbon imprint.

Since 2008 a number of airlines have been conducting tests using biofuels. In February 2008, Virgin Atlantic flew the first test flight between London and Amsterdam using a 20 percent blend of biofuels. The first commercial flight using biofuels was a KLM flight from Amsterdam to Paris carrying 171 passengers since then there have been five other commercial flights using biofuels. The United Airlines flight is the first time biofuels have been tested in the U.S.

While biofuels are environmentally cleaner, the issue of financing this new system has left some aviation companies hesitant to adopt biofuels.

"This is expensive. It's about six times what we normally pay for fuel," said Bill Ayer, chairman and CEO of Alaska Airlines. "So the hope is as this industry develops, and it becomes scalable, the price comes down."

Small scale production of the biofuels has made it more expensive than ordinary jet fuel. Alaska Airlines bought 28,000 gallons of biofuel at $17 a gallon from Dynamic Fuels which is substantially more than the $3 per gallon of jet fuel.

However, Alaska and its regional partners will still add more than 75 flights using biofuels over the next few weeks. United has signed a letter of intent to purchase 20 million gallons per year of the algae biofuel that powered the Boeing 737-800 flight.

The environmental impact of using biofuel is certainly appealing. Alaska Air Group estimates if it used the 20% biofuel blend for all its flights for one year, the emissions savings would be equivalent to taking nearly 64,000 cars off the road.

A sustainable biofuel industry will depend on getting production up and providing more incentives for airlines to use biofuel in their airplanes. The U.S. departments of Agriculture, Energy and the Navy are investing $510 million for commercial scale biofuel production. The program will fund new biofuel plants for the Navy's vehicles and aircraft.