Seventeen percent of the United States’ imported oil for transportation could be replaced by biofuel made from algae, a new study shows.

Research by the Department of Energy's Pacific Northwest National Laboratory (PNNL) shows that being smart about where we grow algae can drastically reduce how much water is needed for algal biofuel.

Growing algae for biofuel, while being water-wise, could also help meet congressionally mandated renewable fuel targets by replacing 17 percent of the nation's imported oil for transportation, according to a paper published in the journal Water Resources Research.

The study also showed that up to 48 percent of the current transportation oil imports could be replaced with algae, though that higher production level would require significantly more water and land.

The team focused its research on the U.S. regions that would use less water to grow algae, those with the nation's sunniest and most humid climates. They found that water use is much less if algae are grown in the U.S. regions that have the sunniest and most humid climates: the Gulf Coast, the Southeastern Seaboard and the Great Lakes.

Algae has been a hot topic of biofuel discussions recently, but no one has taken such a detailed look at how much America could make - and how much water and land it would require — until now, said Mark Wigmosta, lead author and a PNNL hydrologist. This research provides the groundwork and initial estimates needed to better inform renewable energy decisions.

Algal biofuel can be made by extracting and refining the oils, called lipids, that algae produce as they grow. Policy makers and researchers are interested in developing biofuels because they can create fewer overall greenhouse gas emissions than fossil fuels. And biofuels can be made here in the United States. In 2009, slightly more than half of the petroleum consumed by the U.S. was from foreign oil.

The researchers found that 21 billion gallons of algal oil, equal to the 2022 advanced biofuels goal set out by the Energy Independence and Security Act, can be produced with American-grown algae. That's 17 percent of the petroleum that the U.S. imported in 2008 for transportation fuels, and it could be grown on land roughly the size of South Carolina. But the authors also found that 350 gallons of water per gallon of oil — or a quarter of what the country currently uses for irrigated agriculture — would be needed to produce that much algal biofuel.

Algae could be part of the solution to the nation's energy puzzle — if we're smart about where we place growth ponds and the technical challenges to achieving commercial-scale algal biofuel production are met, Wigmosta said.

The team is also researching greenhouse ponds for use in colder climates, as well as economic considerations for algal biofuel production.