The highway funding bill proposed Tuesday would be partially funded by selling oil from the nation's emergency petroleum stash, underscoring the increasing number of lawmakers who have come to view the reserve as a potential piggybank.

The measure, brokered between Senate Majority Leader Mitch McConnell and Democratic Sen. Barbara Boxer of California would sell 101 million barrels to generate an estimated $9 billion.

Both Democrats and Republicans say that selling off some of the Strategic Petroleum Reserve, which contained nearly 694 million barrels of oil as of June 26, according to McConnell's office, could help pay for other priorities.

A House-passed healthcare bill that included billions of extra dollars for the National Institutes of Health and the Food and Drug Administration, for example, would get part of its funding by selling 70 million barrels from the reserve.

Republicans on Tuesday said they didn't think including the Strategic Petroleum Reserve as a funding source set a precedent that the supply was open for business.

"I don't call that setting a precedent if it's one-time shot that you do to make an adjustment for an economy that's changed," said Senate Environment and Public Works Committee Chairman Jim Inhofe, R-Okla., whose committee has jurisdiction over highway funding.

The reserve has been used three times, most recently in 2011. It was designed to ward off major supply shocks following the 1973 Arab oil embargo.

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Lawmakers have been eyeing the oil reserve because a rise in U.S. oil production means the federal government doesn't need to keep as much stored for emergency purposes to comply with membership rules set by the International Energy Agency. The U.S. must maintain a reserve supply equal to 90 days of net imports. That amount has lessened as domestic production has replaced foreign crude.

For Democrats, the Strategic Petroleum Reserve is just one of many funding sources with which they might disagree. Though they said they needed more time to review the 1,000-plus page bill, Democrats said they were generally wary of relying on a hodgepodge mix of sources to fund highways.

"Historically we have paid for these things through some sort of user fee, and I think that approach has made a lot of sense. And so I have general concerns paying for long-term transportation infrastructure investments by piecemealing a number of unrelated things together in terms of pay-fors. And I think that's been a negative trend," Sen. Martin Heinrich, D-N.M., told the Washington Examiner.

The highway bill contains three years of guaranteed highway funding, which is set to run out at the end of the month without new legislation. Democrats blocked a procedural move Tuesday that would have allowed the Senate to begin debating the bill, as the minority party said it needed more time to read the legislation.

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The oil sell-off would begin with 4 million barrels in fiscal 2018, eventually rising to 25 million in 2025. McConnell and Senate Environment and Public Works Committee ranking member Sen. Barbara Boxer, D-Calif., who brokered the deal with the Kentucky Republican, are counting on oil prices to rise. West Texas Intermediate, a U.S. oil benchmark, was trading at about $50 per barrel Tuesday, which would generate just over $5 billion if prices held steady.

White House spokesman Josh Earnest didn't dismiss the idea of using the reserve to pay for the highway bill, though he didn't endorse it.

"At the risk of unintentionally suggesting to some people who are closely watching the energy markets that this may be telegraphing a decision about a sale, I don't have a specific comment on that," he said at a Monday press conference.

Democrats have traditionally resisted tapping the reserve as a funding mechanism. And not all Republicans are on board, either. Senate Energy and Natural Resources Committee Chairwoman Lisa Murkowski cautioned against doing so, though she was open to selling from the reserve if it would advance energy security.

"If we're going to erode our energy security and our national security through a one-time quick sale for asphalt, is that smart policy? I don't think so," the Alaska Republican told reporters.

But Inhofe said Murkowski was the only Senate Republican he knew of who had a significant problem with raiding the reserve.

"I think [the reserve] is much larger than it should be. I've had that conversation with them and most of them are pretty much in agreement with that. Lisa Murkowski might be the only one who's opposed to it," Inhofe said.