"From Barracks to Battlefield: Clean Energy Innovation and America's Armed Forces" by Pew Charitable Trusts indicated that such spending from 2006-09 rose 300 percent, from $400 million to $1.2 billion.
In 2010 the Defense Department's total energy cost was $15.2 billion, with 74 percent for operations and 26 percent for facilities.
In the past half-century, the amount of fuel needed to support each deployed U.S. service personnel has risen from 5 gallons a day to more than 22 gallons, the Pew study says.
While the military uses more than 300,000 barrels of oil a day, it aims to obtain 25 percent of its energy from renewable sources by 2025.
"There are great strategic reasons for moving away from fossil fuels: It's costly," said Navy Secretary Ray Mabus, a former ambassador to Saudi Arabia, at the National Clean Energy Summit in Las Vegas last month.
"Every time the cost of a barrel of oil goes up a dollar, it costs the United States Navy $31 million in extra fuel costs."
Specific Department of Defense goals outlined in the Pew study include for the U.S. Navy to reduce ship fuel consumption by 15 percent by 2020 compared to 2010 levels; for the U.S. Air Force to rely on biofuels for 50 percent of its domestic aviation needs by 2016 and for the Navy and Marines to each get 50 percent of energy needs from alternative energy sources by 2020.
Aside from the cost, the Pentagon's push for green energy stems from the risks of transporting liquid fuels to combat areas and the impact fuel availability has on the effectiveness of military operations.
In Afghanistan and Iraq, for example, fuel shipments account for 80 percent of all supply convoys, with as many one in 46 convoys suffering a casualty in 2010.
"As one of the largest energy consumers in the world, the Department of Defense has the ability to help shape America's energy future," said Phyllis Cuttino, director of the Pew Clean Energy Program.
"(The Department of Defense's) efforts to harness clean energy will save lives, save money and enhance the nation's energy and economic future."
Retired U.S. Sen. John Warner, R-Va., who is a former chairman of the Senate Armed Services Committee and former secretary of the Navy, oversaw the study. He is a senior adviser at Pew.