Cable TV surpassed $10 billion in ad commitments in this year's upfront negotiations for the new season of programming, once again topping broadcast prime-time, according to the Cabletelevision Advertising Bureau, a trade group for the cable industry. But growth is slowing, with ad-supported cable networks adding just $400 million to last year's total.

Ad-supported cable networks secured approximately $10.2 billion, a 4.3% increase from the year prior, the Cabletelevision Advertising Bureau said in a report compiling figures from its members. That's a smaller boost than in 2012, when it jumped 5% to about $9.8 billion from $9.3 billion, and well below the double-digit percentage increases of 2011 and 2010.

The $10.2 billion overwhelmingly reflects commitments for commercial time in traditional cable TV programming and video on demand play, said Sean Cunningham, CEO of the Cabletelevision Advertising Bureau. Cable networks also secured roughly $500 million in online video deals, he said.

This was the first year the bureau asked its members to supply totals for online video ad commitments from its members. It didn't include the online sum in the total $10.2 billion figure because of a lack of consistency among members in reporting the amounts, Mr. Cunningham said.

Cable TV continues to surpass broadcast, with the Big Four broadcasters and The CW securing between $8.7 billion and $9.3 billion in the 2013 upfront, in line with last year's range of $8.8 billion to $9.3 billion, according to Ad Age estimates.

There are just five broadcast networks, of course, but their upfront ad haul still topped cable's total commitments just a few years ago.

Broadcasters have been contending with declining ratings and an increase in quality programming on cable and other non-traditional platforms. Advertisers also held back more money during talks this year, money that could reappear in the "scatter" marketplace where ad time is bought and sold closer to the air date.