Updated 5:50 p.m. ET



Restore Our Future, a super PAC aiding Mitt Romney, raised $6.6 million in January to aid his presidential campaign, documents filed today show.

The super PAC spent nearly $14 million in January as it blistered Romney's GOP rivals with stinging ads during last month's caucuses and primaries. It ended the month with $16.3 million in the bank, some of which is being deployed in Romney's native state of Michigan ahead of the Feb. 28 primary there.

By comparison, the super PAC supporting Newt Gingrich raised slightly more than $11 million last month -- nearly all of it from casino mogul Sheldon Adelson and his wife, Miriam.

The details of the super PAC's fundraising emerged as Republican presidential candidates and the other super PACs active in this year's election file January fundraising reports to the Federal Election Commission today.

Winning Our Future, the pro-Gingrich super PAC, reported spending about $9.8 million on its federal election activities, the group's documents show. It had about $2.4 million cash on hand.

Adelson, who owns the Venetian on the Las Vegas strip, and his wife, Miriam, a physician, each donated $5 million to the super PAC.

Overall, Restore Our Future has raised nearly $36.8 million since it was created last year. January donors include Texas billionaire Harold Simmons, who gave $100,000, and members of the Marriott and Walton families, who established the hotel chain and Walmart stores, respectively. Meg Whitman, who ran unsuccessfully for California governor in 2010, also donated $100,000 to Restore Our Future last month.

A report filed earlier today showed PayPal co-founder Peter Thiel donated $1.7 million last month to a super PAC supporting one of Romney's GOP rivals, Ron Paul.

Overall, Thiel has donated $2.6 million to Endorse Liberty, created last year to aid the Texas representative.

The latest FEC reports are expected to show a sharp uptick in fundraising for former Pennsylvania senator Rick Santorum, who raised less than $2.2 million in 2011 before winning a string of contests early this year. He now leads Mitt Romney in the latest public polls in Michigan.

On Friday, President Obama reported a sharp drop from four years ago in his fundraising. He collected $29.1 million for his campaign and the Democratic National Committee in January. Nearly $11.9 million went into his campaign account, a third of what he raised as a candidate in January 2008.

Today's filings are giving the public a picture of how much a handful of unions, corporations and wealthy individuals can shape super PACs, new outside groups raising and spending unlimited amounts to influence the presidential contest and other races.

Jon Huntsman Sr., the billionaire father of former GOP candidate Jon Huntsman, donated another $335,000 in January to Our Destiny PAC, a super PAC that supported his son's failed candidacy, the reports show. In all, the elder Huntsman gave $2.2 million to the super PAC, nearly 70% of the total it collected.

The reports are due by midnight.

(Contributing: Ray Locker)