The analysis by the Wesleyan Media Project said about 17% were positive, and 26% contrasted the two candidates.
The race between Mitch McConnell and Alison Lundergan Grimes could turn out to be the most expensive U.S. Senate race in American history.
According to the Center for Public Integrity, Republicans had outspent Democrats by almost $8.5 million.
It would mean that voters had watched about 13,600 more television ads for McConnell than they had for Grimes.
The news organization said that Grimes had aired more than 30,700 ads in her campaign.