ethanol gas cap

The boxing match between ethanol supporters and opponents is heading into the final round, and it's looking like ethanol could go down pretty hard.

The US Environmental Protection Agency's 60-day public comment period for its proposed Renewable Fuel Standard (RFS) policy changes – which have eased off the ethanol pedal a bit, for the first time ever - comes to a close in mid-January. While many of the major automakers are already manufacturing 2014 model year vehicles that are capable of burning 15-percent ethanol-blended gasoline (E15), it doesn't look like very much of that biofuel will be showing up at gas stations. There's the debate over E15's effect on engines, and now federal support for corn ethanol could be going away.

Last month, US Senator Dianne Feinstein (D-CA) joined forces with Senator Tom Coburn (R-OK) to introduce a bill that would remove ethanol from the RFS. Feinstein remains a supporter of renewable fuels, she says, but told CNBC it's "really not wise" to make too much of it. She's also worried about the effects on livestock producers in her home state.

Of course, ethanol advocates don't agree at all with proposed bill's assumptions. "This measure would strand billions of dollars already invested in advanced fuels; undermine research and development; and threaten thousands of potential jobs," said biofuels advocacy group Fuels America in a statement.