On May 6, 2014, in what is largely seen as a win for the U.S. Environmental Protection Agency (EPA) and the biofuels industry, the U.S. Court of Appeals for the District of Columbia Circuit rejected the challenge to EPA's final 2013 Renewable Fuel Standard (RFS) rule by Monroe Energy, LLC (Monroe Energy), a refinery and subsidiary of Delta Airlines. In Monroe Energy, LLC v. EPA, the court held that EPA properly utilized its authority under the federal RFS to set the 2013 RFS volume requirements. The court disagreed with Monroe Energy that EPA did not sufficiently consider factors in setting the final 2013 RFS rule, including the means of compliance for obligated parties. Further, the court held that the RFS provides EPA wide discretion under its cellulosic waiver provision. As such, it was within EPA's discretion to decide against lowering the overall or advanced 2013 RFS requirements when it lowered the 2013 cellulosic requirements using that authority.

The May 6 decision did not include challenges to EPA's final 2013 RFS rule related to overall, advanced, and cellulosic biofuel requirements of the American Petroleum Institute (API) and American Fuel & Petrochemical Manufacturers (AFPM). The court severed the API and AFPM challenges to the 2013 rule from Monroe Energy's challenge to the same rule. The court had earlier agreed to sever and hold in abeyance challenges to the cellulosic biofuel requirement under the 2013 rule while EPA reconsidered it.