The super PAC backing Mitt Romney's presidential run retained its place as the number one super PAC, in terms of financing, as it pulled in an additional $3.85 million in April, according to a report filed Sunday with the Federal Election Commission (FEC).

Contributions continued to flow into the group from the financial industry, with at least $1.77 million coming from individuals working in the sector. Romney's campaign has traded on his connections in the finance world to pull in millions from the employees of big banks, hedge funds and private equity companies. The same is true of the super PAC run by his supporters.

Restore Our Future has raised at least $28.6 million from the finance, insurance and real estate sectors through the end of April, according to a review of the group's May filing and numbers provided by the Center for Responsive Politics.

The biggest financial sector donation in April was a $1 million contribution from the Texas-based investor John Kleinheinz, a first-time donor to super PACs. Other notable contributions from the financial sector include $250,000 from Bain Capital's Stephen Zide and $100,000 each from Sun Capital Advisors' Marc Leder and Roger Krouse.

The energy industry, particularly oil and gas companies and their executives, has provided a hefty amount of money to the super PAC, as well. In April, the CEO of Continental Resources, Inc., which bills itself as "America's Oil Champion," Harold Hamm gave Restore Our Future $985,000. The Hallador Energy Company, one of only four corporations contributing to the super PAC, gave $100,000. Another energy company, United Refining, gave $25,000.

Other big donors in April include Select Medical's Rocco Ortenzio ($250,000), Limited Brands CEO Leslie Wexner ($250,000), oil and real estate heiress Marjorie Fisher ($100,000) and retired Panduit head Jack Caveney ($100,000).

The group also received a $750,000 check from its top donor, Texas homebuilder Bob Perry, but refunded the contribution a few weeks later. Perry had already given the group $4 million.

Restore Our Future, which can raise unlimited sums of money from corporations, unions and individuals, was an invaluable weapon in Romney's campaign arsenal during his run through the Republican Party presidential primaries.

Beginning in December, the group spent more money than any other independent group in a presidential primary campaign in recorded history to pummel Romney's opponents with negative attack ads. Newt Gingrich first faced the wrath of the super PAC, as the group spent nearly $3.5 million on attack ads that targeted the former Speaker of the House before the Iowa caucuses. After Gingrich faded and former Pennsylvania Sen. Rick Santorum rose as a challenger, the super PAC shifted its spending to hammer Santorum in the Super Tuesday states and later in Ohio, Michigan and elsewhere.

By the time Santorum and Gingrich ended their campaigns, Restore Our Future had spent $21 million and $18 million, respectively, against the two candidates.

Since the primary has ended, the super PAC has purged its YouTube page of the negative attack ads run against former rivals Gingrich and Santorum, presumably to rebrand itself as a pro-Romney and anti-Barack Obama group, although it has yet to cut a fully negative attack ad against the president.

The group has already turned to the general election, having announced in May an advertising campaign, focused largely on positive spots promoting Romney, that will total $4 million. The super PAC certainly has enough money to keep going after reporting $8.2 million cash on hand at the end of April.

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