Carbon-dioxide emissions from jets are a growing environmental concern. In the United States, about 12 percent of carbon-dioxide emissions come from jet fuel, a rate that is expected to rise as air travel increases. In addition, fuel prices have more than doubled from 2000 to 2006, boosting airline operating costs and making airlines increasingly desperate for a more price-stable alternative.

But designing less-polluting new jet fuels is a challenge. Such a fuel must have a freezing point low enough to withstand high-altitude temperatures and an energy density high enough to allow planes to fly long routes without added weight--two requirements that take currently available biofuels out of the running. Ethanol has a low energy content and other problematic properties, and biodiesel's freezing point is too high.

A new biofuel under development by Amyris Biotechnologies, a startup based in Emeryville, CA, could fill that hole. The company's approach is to engineer the metabolic system of microorganisms to create a variety of specialized hydrocarbons. To date, the company has successfully created microbes that can pump out the precursor for a crucial malaria drug called artemisinin. (See "Cheaper Malaria Drugs.") Spurred by interest from the British megaconglomerate Virgin, which has recently launched a fuel division, Amyris has put a new focus on a cost-competitive jet fuel. Amyris scientists say they can now produce hydrocarbons with properties that rival the current jet-fuel industry standard, a kerosene-based product known as jet-A. The microbial factories ferment sugar to produce hydrocarbons, a process that has significantly less impact on global warming than traditional fuel production.

Amyris CEO John Melo, formerly president of U.S. Fuels Operations for British Petroleum, talks with TR about the company's progress.

Technology Review: Why is Virgin so interested in alternative jet fuels?

John Melo: Carbon taxes are coming into play for air travel in Europe, and they are concerned that this is the beginning of a trend that, if it took hold, would significantly take away profit from airlines. In addition, fuel is such a big driver of profit contribution to airlines, they see having an alternative as a critical issue for the future of air travel. Demand growth for jet fuel is about three times the demand growth of gasoline.

We had not given jet fuels a lot of thought until Virgin approached us towards the end of last year. They had learned about what we were doing and wanted to explore if our technology could be used for jet fuel. The fact that no one else was addressing the problem in a sustainable way focused us on the problem. We realized we could make a big impact if we developed a fuel with zero sum carbon emissions.