The Energy Department has a gas problem.

At two of the department’s outposts, the Los Alamos National Laboratory and the Bonneville Power Administration, a large fleet of supposedly environmentally-friendly  flex-fuel cars were routinely filled with regular old gasoline (read: not so green), an inspector general report found.

The report dinged the managers of the cars, noting that they had “not always managed their substantial vehicle fleets in a cost-effective or efficient manner, nor did they take all prudent steps to advance the use of alternative fuels.”

And the flex-fuel cars cost an extra $700,000 over what the department would have spent on traditional gas-guzzlers.

In some cases, the report notes, it was tough to find the ethanol to power them. So at one point, the folks at Los Alamos used a tanker truck to bring ethanol fuel to 65 vehicles, which cost $66,000.

As Kermit might have said, it isn’t easy — or cheap — being  green.