The pro-Romney super-PAC Restore Our Future spent $14 million in January, according to documents filed with the Federal Election Commission on Monday.

That’s more than twice the nearly $7 million the super-PAC raised in January, although Restore Our Future finished the month with more than $16 million in the bank, according to a report in The New York Times.

The bulk of the fundraising came from wealthy donors, including Marriott International Chairman J.W. Marriott and Hewlett-Packard CEO Meg Whitman, with three individuals contributing $500,000 each.

Restore Our Future has raised more than $36 million in this election cycle.

With their fundraising advantage, the Romney campaign and associated super-PAC have managed to flood markets in key primary states with campaign advertisements, hitting their GOP opponents. Many have attributed Romney’s heavy spending in Florida’s expensive media markets for sinking the Newt Gingrich campaign following his convincing victory in the South Carolina primary.

The super-PAC has now turned its sights on Rick Santorum ahead of the hotly contested Michigan and Arizona primaries later this month, portraying the former Pennsylvania senator as a lifelong Washington insider who contributed to the culture of overspending and waste.

Last week, the Romney campaign also unveiled an ad in Michigan hammering Santorum over his record on earmarks.