Biofuels are held up as a relatively easy solution to the twin problems of petroleum dependence and carbon emissions. But new research suggests that fuels such as corn-based ethanol may cause as many problems as they solve. Clearing new land and converting existing cropland to certain fuel feedstocks can actually incur a "carbon debt," causing more carbon to be released than is saved by the production of biofuels, a scenario that could aggrevate global climate disruption. Other biofuel options that are more carbon neutral include fuels using cellulosic feedstocks or algae. Such low-carbon biofuels could counter the problems posed by conventional biofuel crops, with the caveat that policy makers and industry must be prepared to act promptly and decisively to foster a truly sustainable biofuel market.