LONDON — Boeing Co., the world's second-biggest maker of commercial aircraft, said its planes may be flying on a mix of biofuel and jet kerosene within five years.

The U.S. company has been examining the use of alternative fuels for two years, environment director Billy Glover said last week in an interview in London. A Virgin Atlantic Airways Ltd. Boeing 747 is scheduled to make the first biofuel-powered test flight for a commercial plane later this month.

Boeing is focusing on so-called second-generation biofuels that would be more environmentally friendly, Glover said. Algae has the "highest yield potential," he said, with oil from Babassu nuts, grown in South America, and the hardy Jatropha bush also being considered. First-generation fuels such as vegetable oil may use up scarce water resources and compete with subsistence food crops in poorer countries.

"I think we're going to have a commercial product within about five or six years," Glover said. The percentage of biofuel in the blend will initially be "fairly low" because of the difficulty in producing it, he said.

Boeing aircraft could fly on a blend of biofuel and traditional jet kerosene without additional equipment, he said. The new energy source would need to be available at a price airlines were able to afford, he said.

"It can't be much more expensive, if any," Glover said. "How it's going to be price-competitive will depend on the processes selected, it'll depend on policy elements around biofuel, whether or not there's any assistance."

Toulouse, France-based Airbus SAS, the biggest jetliner manufacturer, tested gas-to-liquid fuel on Feb. 1 on an A380 superjumbo, the first flight of a jetliner using an alternative to kerosene. Airbus described the technology as a precursor to biofuel, which it said it would use once available. Chicago-based Boeing has no plans to explore GLS technology, Glover said.

Air New Zealand Ltd. is also working with Boeing and will test flights this year or in early 2009 using a different type of biofuel to that trialed by Virgin, Glover said. The Virgin plane will fly with a blend of 20 percent biofuel, though the mix for the first revenue-earnings flights would initially be lower than that, he said.

Biofuels used in ground transport have been introduced with a mix of less than 5 percent, a level that would result in a 2.5 percent reduction in emissions, Glover said, since the fuel generally emits about half as much pollution as petroleum.

"It's a start but it will take time to go further," the environment director said. "Someday we might see 100 percent biofuel and then we'll have a 50 percent reduction, roughly."