World's First Bio-fuel Jet

``Two years ago, people said that was impossible. They said it would freeze at 30,000 feet,'' Branson said in an interview. Today's test was ``purely'' to prove biofuel will work on commercial aircraft, he said.

Branson said he views algae-derived fuel as the most promising because it can be produced in large quantities without harming the environment. The fuel source used today isn't plentiful enough to be a major resource for the airline industry he said.