It's a good thing audiences like to watch ads during the Super Bowl: every year there are more of them.

According to a new report from TNS Media Intelligence, ad clutter in sports television's biggest annual event has been creeping upwards for the last 11 years.

The 2006 Super Bowl featured 47 minutes and 20 seconds worth of ads, a 30% increase over the 1996 games.

It's not hard to figure out why.

"As rights fees [for the games] have escalated, ad clutter has escalated," says Jon Swallen, senior vice president of research for TNS. "Networks can increase the price, but adding ad time is a more palatable way of making the economics work."

Despite the increased volume of ads and the gradually declining ratings for the event, Super Bowl ad prices have continued to climb. In 1987, a 30-second unit cost an advertiser $600,000. This year the same unit is expected to cost $2.6 million, a slight increase over last year's $2.5 million.

Mr. Swallen credits the price increases to savvy marketing by the networks and the National Football League, and the fact that it's harder than ever for marketers to reach a large audience.

"There's the cachet of the Super Bowl itself," he says of the pricey ads. "And it's still the single largest audience in television by a wide margin."

That's one reason the event's biggest category of advertiser isn't beer or cars, but promotional spots for the host network's own shows. Last year, 22% of all ad time in the Super Bowl was devoted to network promotions.

"Over the long haul, the potential ad revenue windfall you can generate from your regular series programming is much greater than what you can generate from a one-time event," Mr. Swallen explains.