Between Sept. 9 and Sept. 30 - from the end of the political conventions to the first debate between President Barack Obama and GOP challenger Mitt Romney - the two campaigns and their supporters aired ads 7,770 times in Denver, according to the Wesleyan Media Project.
Ads supporting Obama aired 1,812 more times in the city than ads supporting Romney, according to the authors, who analyzed data compiled by the private group Kantar Media/CMAG.
Obama and Democratic groups paid to air their ads 4,791 times. The Obama campaign paid for 4,001 of those spots and independent Democratic groups paid for 790, the analysis found.
The Romney side aired its ads 2,979 times. The former Massachusetts governor's campaign paid for 1,470 of the spots, independent GOP groups paid for 1,393 and the Republican National Committee paid for 116.
Obama's more frequent presence on Colorado airwaves likely explains why he has been leading Romney in Colorado, according to the Wesleyan Media Project.
He was up an average of 3.1 percentage points in the state, according to the Real Clear Politics online political site. But that was before Wednesday's debate at the University of Denver, which Romney is widely seen as having won.
Colorado has nine electoral votes.
"The heavy advertising from the Obama campaign has challenged the assumption that Romney-friendly outside groups would saturate and dominate the airwaves in key markets," Erika Franklin Fowler, co-director of the Wesleyan Media Project and a political scientist at Wesleyan University in Connecticut, said in a statement.
Ads by both sides were predominantly negative in swing states.
The Obama campaign ran ads 2,000-3,000 times in September in most other major markets elsewhere in the country.
The campaign likely decided to run more ads in Denver because internal polls showed the race is very close in Colorado, said Travis Ridout, another Wesleyan Media Project co-director and a Washington State University political scientist.
"The Denver area is where their potential voters lie, where you'll find the soccer moms, the swing voters, the independents who could go either way," Ridout said in an interview.
Presidential ads weren't restricted to Denver.
Democratic ads were shown 322 more times than GOP ones in conservative Colorado Springs and 693 more times in Grand Junction, the Wesleyan Media Project found.
Kim Parker, an Obama campaign spokeswoman in Colorado, refused to discuss advertising strategies for the rest of the election season. The president's campaign released a new ad Thursday questioning Romney's tax plan.
Representatives of the Romney campaign in Colorado did not respond to requests for comment.
Obama and his allies made more ad buys in the swing states of Colorado, Florida (29 electoral votes), Ohio (18 electoral votes), and Virginia (13 electoral votes) last month, the Wesleyan Media Project found. Those states, especially Ohio and Florida, are seen as holding the keys to the election.
By RAJU CHEBIUM, Gannett Washington Bureau
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