Republican nominee Mitt Romney and his allies are banking heavily on a high-risk, high-reward media strategy in the final weeks of the campaign, hoping that burying President Barack Obama in ads will give them a crucial edge on Election Day.

Ad purchases in the presidential race doubled or in some cases tripled last week in swing states such as Iowa, Colorado, Florida and Virginia, tracking data show. The surge is being driven by Romney and well-funded allies, who decided against running more ads earlier in the campaign in favor of a big bang at the end.

Restore Our Future, a super PAC dedicated to helping Romney, has booked $14 million worth of ads in nine states for the final week of October — more than it spent on ads during the entire month of September. The group is also ramping up its spending, airing a mix of ads criticizing Obama and extolling Romney in Iowa, Florida, Michigan, Ohio and Virginia.