Continued pressure on ethanol margins is forcing biofuel refiners to re-evaluate their operation amid mounting losses. Omaha-based Green Plains Inc. announced last week that it is permanently closing its 60-million-gallon-per-year ethanol plant in Virginia. Green Plains, the fourth-largest ethanol producer in the U.S., reported a net loss of $12.5 million in the third quarter.

Two other ethanol plants have also recently shut down, as Ergon BioFuels LLC said it would permanently close its only ethanol plant ...