President Barack Obama and his supporters flooded the Dayton airwaves during the last three weeks of last month, airing 2,112 television spots on Dayton TV stations compared to Republican presidential nominee Mitt Romney’s 1,746.

In all, that meant Dayton viewers saw 366 more ads supporting Obama than they did for Romney, according to a report released Wednesday by the Wesleyan Media Project, which tracks political advertising. Sixty-six percent of those ads were negative, the study found.

The project found that nationally, Obama held an advertising advantage in 14 of the 15 most-advertised media markets in Virginia, Ohio and Florida. And in Ohio, viewers in every TV market except Wheeling saw more ads supporting Obama than they did Romney.

The same study revealed that Ohio had the most expensive House and Senate race in the country.

In the top 15 TV markets, Romney and pro-Romney ads outpaced Obama and pro-Obama ads only in Las Vegas. The study tracked Sept. 9 through Sept. 30, beginning at the conclusion of the Democratic National Convention.

The study challenges the argument that outside groups friendly to Romney would dominate the airwaves: Between Sept. 9 and Sept. 30, Obama and groups supporting Obama aired 93,389 ads in key swing states, compared to the 69,952 ads aired by Romney and pro-Romney groups. Obama and his supporters spent more than $45 million to $43.5 million for Romney during the period.

That’s been the case throughout the campaign. Nationally, Obama has aired 363,010 ads in swing states since April compared to the 126,748 ads aired by the Romney campaign.

It isn’t the case, however, in the U.S. Senate race in Ohio, where Republican Treasurer Josh Mandel and groups supporting the Republican spent $3.4 million to the nearly $2.6 million being spent by the Brown campaign and Brown supporters between Sept. 9 and Sept. 30. That translated to 4,669 ads for Brown during that period and 5,390 for Mandel, according to the analysis.

The Ohio Senate race was the nation’s costliest in terms of TV airtime last month, with a total of $6 million spent on TV ads there compared to $5.9 million in the Senate race between Sen. Scott Brown, a Republican, and Democrat Elizabeth Warren.

Ohio also laid claim to the costliest House race last month. In northeast Ohio’s 16th District, where Democrat Betty Sutton and Republican Jim Renacci are fighting over a newly-drawn district, TV viewers were shown 1,944 ads last month totaling $2.1 million — more than in any other top 50 TV market in the country.