Gevo did not immediately respond to queries about what role, if any, Khosla played in helping the firm secure government grants or contracts.

Republicans upset over Navy spending on biofuels are backing legislation that could bar the Pentagon from contracting for fuels that are more expensive than traditional petroleum, something that worries military officials.

The officials agree that purchases for operational quantities of fuel should be at competitive prices, but they warn that legislative language could restrict them and ultimately make it difficult for them to economize.

“Congress has been very vocal in not wanting us to pay a huge premium to use alternative fuels. I get that,” Geiss said.

“Our goal is that it’s got to be cost-competitive. But cost- competitive doesn’t mean that you’ve got a bright line that you can’t even .... (exceed by) a penny. I think in trying to define these lines, they may be presenting some challenges for us,” he said.

Supporters of the alternative fuel industry argue that green energy spending will eventually help cushion price volatility. They have begun to push back against Republican criticism.

A coalition of groups, including the powerful American Farm Bureau Federation, bought full-page ads in a Capitol Hill publication this week with glossy photos of biofuels success stories.

Those featured Gevo’s Luverne, Minnesota, plant for producing isobutanol, an alcohol that can be added to gasoline like ethanol or processed into other chemicals.

Adm. Jonathan Greenert, chief of naval operations, and a group of retired senior officers briefed about 100 Senate staffers on Thursday about the Navy’s use of alternative fuels.

Dan Nolan, a retired Army colonel, said biofuels were currently too expensive to purchase in operational quantities but it made sense to begin testing because “strategically if we can start moving toward that … it’s going to be worth every penny we invest in it now.”