Long-awaited Renewable Fuel Standard program revisions that the EPA released late last month indicate that while the federal agency has no plans to reverse corn ethanol's presence in the U.S. fuel supply, EPA officials also don't support blending as much total ethanol into fuel as it once did.

Expected in 2013, the proposed RFS volumes of renewable fuels-which include both advanced biofuels and corn-derived ethanol-stipulate 15.93 billion total gallons for 2014, 16.3 billion gallons for 2015, and 17.4 billion gallons for 2016. The EPA derived all the 2014 volumes from actual amounts put onto the market last year.

Those numbers fall short of the total volumes the EPA initially proposed five years ago by 2.22 billion gallons for 2014 (12 percent), 4.2 billion gallons for 2015 (20 percent), and 4.85 gallons for 2016 (22 percent). Analysts point to a number of factors for the revised projections, including the effects of hitting the E10 blend wall, reduced demand for gasoline in general, and slower adoption of advanced biofuels (cellulosic biofuel, for example, comprised just 33 million gallons of the 2014 totals, versus a projected 1.75 billion gallons).

See why the EPA is cutting back its E15 expansion.