Federal regulations require refiners to begin and then stop producing summer-blended gasoline by a specific date, preventing a phase-in period that could let firms avoid having to completely empty their storage tanks so there is no mixing of summer-blended and winter-blended fuels.

"I understand that the EPA will come out with an acknowledgment that the off-the-cliff compliance date that they had for switching to all or nothing (is) as a problem and there's some talk about smoothing that, which I think will help," Cavaney said.

The switch-over period often results in spikes in gasoline prices - especially in Midwest states - as motor fuel supplies suddenly drop at the beginning of the summer driving season, which do not ease until refiners build inventories of less-polluting blends.

Cavaney said he understands the EPA will recommend that refineries be given "somewhere in the neighborhood of several weeks" to switch into production of seasonal gasoline blends.

"It's not hugely long. We don't need a whole lot of time," he said.