In a push to find better biofuels to reduce gasoline consumption and lower greenhouse-gas emissions, scientists have genetically engineered E. coli that is highly efficient in producing butanol, a promising new type of biofuel. The new technology could speed up the development of butanol biofuels into a cost-effective alternative to ethanol.

While ethanol is the main biofuel on the market today, energy firms are increasingly looking to alternatives such as butanol. “It has many attractive properties,” says Jim McMillan, manager of biorefining process R&D at the National Renewable Energy Laboratory’s National Bioenergy Center, in Golden, CO. Because butanol packs more energy per gallon than ethanol does, cars running on butanol get better mileage. And, unlike ethanol, it doesn’t mix with water, so it can be shipped in existing petroleum pipelines without causing problems.