Biofuels may pollute the environment much more heavily if the process used to make them isn't done in the right way, researchers say.

Conventional fossil fuels may sometimes be much greener than their biofuel counterparts, according to a new study.

University Research funded by a pair of U.S. federal government agencies found that taking into account a biofuel's origin is important.

Massachusetts Institute of Technology researchers say, for example that conventional fossil fuels may sometimes be the greener choice compared with fuel made from palm oil grown in a clear-cut rainforest.

What we found was that technologies that look very promising could also result in high emissions, if done improperly, said James Hileman, a an engineer at MIT who published results of a study with graduate students Russell Stratton and Hsin Ming Wong.

You can't simply say a biofuel is good or bad - it depends on how it's produced and processed, and that's part of the debate that hasn't been brought forward.

The study was funded by the Federal Aviation Administration and Air Force Research Labs.

The study includes a life-cycle analysis of 14 fuel sources, which include conventional petroleum-based jet fuel and biofuels which can include biofuels that can replace conventional fuels with little or no change to existing infrastructure or vehicles, according to the report.

Factors used to calculate emissions include acquiring the biomass, transporting it, converting it to fuel and combustion.

All those processes require energy, Hileman says, and that ends up in the release of carbon dioxide.

Biofuels derived from palm oil emitted 55 times more carbon dioxide if the palm oil came from a plantation located in a converted rainforest rather than a previously cleared area, according to the report.

Biofuels could ultimately emit 10 times more carbon dioxide than conventional fuel, the report found.

Severe cases of land-use change could make coal-to-liquid fuels look green, Hileman said. He added that by conventional standards, coal-to-liquid is not a green option.

The research may have applications for industry as companies consider using biofuels, Hileman says.

One solution could be to explore crops such as algae and Salicornia that don't require deforestation or fertile soil to grown, according to Hileman. Neither requires fresh water.