Midwest refineries are cutting production, posing another threat to already battered oil prices.

The Wall Street Journal reports that refiners are awash in gasoline and other fuels and have little choice but to slow production. The Midwest processes nearly 25 percent of U.S. crude. With the refiners’ usage reduced, more oil remains in the market, swelling the glut that cratered crude prices.

The refineries had been processing as much oil as possible, so the slowdown represents a significant change.