The proposal, expected to be made final by Nov. 30, will “establish a path for ambitious, responsible growth in biofuels and help provide the certainty that the market needs to allow these low-carbon fuels to further develop,” she said.

Industry critics and environmental groups alike blasted the proposal, saying that the proposed mandates point to the need for congressional action to rework or repeal the RFS.

Jack Gerard, American Petroleum Institute president and CEO, told reporters on May 29: “EPA assumes growing demand for high-ethanol fuel blends that are not compatible with most cars on the road today…The announcement makes abundantly clear that the only solution is for Congress to repeal or significant reform the RFS.”

He added that lawmakers from both parties have expressed frustration with the current RFS.

Moreover, some environmental groups find the ethanol mandate problematic. The Environmental Working Group released a report in 2014 that said the idea that ethanol, a corn-based fuel, would lower greenhouse gas emissions, has not lived up to its promise.

In fact, a 2014 report from Environmental Working Group suggested that U.S. greenhouse gas emissions could be lowered by millions of metric tons annually if the corn ethanol mandate were reduced or repealed.

However, Jessie Stolark, Environmental and Energy Study Institute policy associate, says she is “disappointed” that the proposal does not go far enough to incentivize biofuels.

As a result, growth of advanced cellulosic fuels, a nascent but growing part of the fuels sector, will continue to be stifled, she says. “The delay was very chilling, and this [proposal] will give investors very little confidence that this is a growth market,” she says.

She notes that research from the Dept. of Energy’s Argonne National Laboratory has suggested that advanced cellulosic fuels that use algae, as well as agricultural waste and some feedstocks, would not contribute significantly to greenhouse gas emissions and have a much better GHG profile than gasoline.