Jeremy Hobson: The Senate is expected to vote today on a Republican proposal to increase domestic oil drilling. But the chances of passage look about as good as yesterday’s vote on taking away tax breaks for big oil companies which failed. Both proposals are Washington’s way of responding to high gas prices.

And now, as our our Washington Bureau chief John Dimsdale reports, some Senators are calling for an investigation into potential price fixing by the nation’s oil refiners.

John Dimsdale: The group of Democrats say the refineries’ take from each gallon of gasoline has nearly doubled since January.

Charles Schumer: We don’t know if this is a smoking gun, but it sure requires a close look.

New York’s Charles Schumer and Missouri’s Claire McCaskill say refiners are only running at 80 percent capacity. McCaskill wonders whether they are deliberately trimming supply to increase the price.

Claire McCaskill: There’s a 20 percent capacity they’re not using. Obviously, I think most consumers in America would go ‘why not?’

The American Petroleum Institute’s John Felmy says the capacity cutback is due to spring maintenance and flood prevention. As for the gusher of earnings:

John Felmy: It’s important to know that at the beginning of the year, refiners were losing money. So talking about big percentage increases off of very small number is simply bogus.

Still, senators want the Federal Trade Commission to check it out.

In Washington, I’m John Dimsdale for Marketplace.