High US gasoline prices are increasing pressure on the Senate to pass legislation allowing a greater share of corn-based ethanol into the national fuel mix. Last week the House of Representatives passed a bill that would permit the year-round sale of E15, in which conventional gasoline is mixed with a 15% blend of ethanol (usually E15 is banned during summer months over concerns that it contributes to smog).

It’s a rare issue that deeply divides Congressional Republicans, between supporters from corn-producing states and opponents representing states that either produce oil or host small refineries that can see their margins hurt by higher biofuel blends. On Wednesday, Majority Leader John Thune (R-S.D.), an E15 proponent, told reporters he’s “hopeful and confident that in the end we’ll be able to succeed” in passing an E15 bill, which he said would help lower gasoline prices. But Thune’s number two, Sen. John Barrasso (R-Wyo.) was adamant last week that he’s still against it. “It’s unlikely the Senate will take up this bill as a standalone vote like the House did — there’s too much opposition,” Drew Monroe, an analyst at the consulting firm Capstone, told Semafor. “It would need to be attached to a must-pass legislative vehicle; the government funding bills ahead of the Sept. 30 deadline are a potential path forward.”