• by David Goetzl  @dgoetzl, July 22, 2009

Broadcast networks produced a 3.5% increase in the number of combined commercial minutes in prime time last year -- a sign that networks may be forced to squeeze in more spots to keep revenues growing. Nielsen figures show that the total rose to 5,688 minutes in 2008, topping the total of 5,492 the year before.

While prime time saw a notable boost, daytime commercial minutes were about flat, with a total of 3,811 increasing less than 1% over 2007. Daytime covers 10 a.m. to 4:30 p.m.

The figures span the range of English-language broadcast networks, including CW, MyNetworkTV and Ion. Cable is excluded.

Only national-network spots are counted. Local breaks, promos and direct-response ads -- all of which contribute to the proverbial clutter -- are not.

When prime-time and daytime commercial minutes are combined, the 2008 total increases 2.5%. That is close to the 3.5% increase in total revenues (to $17.23 billion) for the Big 4 networks in 2008, according to Universal McCann.

But it is difficult to gauge a correlation because the financial figures also include dollars generated from afternoon weekend sports broadcasts and late-night.

Spanish-language networks saw a much higher increase in commercial load than their general-market counterparts. Total commercial minutes for prime time rose 11% in 2008 from 2,540 to 2,817. Those figures cover Univision, Telemundo, TeleFutura and Azteca America.

Trade groups, the 4As and the ANA, used to publish an annual "Commercial Monitoring Report," or clutter study, that offered some insight into increases in commercial loads and on-air promotions, but it was abandoned around 2001.

While adding commercials can increase revenues, networks may be airing more to provide makegoods to advertisers as ratings decline.