Fewer people have been tuning into some of Viacom Inc.'s VIAB +0.88% cable channels over the past year, so the company has turned to a timeworn but controversial method of maintaining ad revenue: adding more commercials.
According to data from TV-research firm Nielsen, the media conglomerate's Nickelodeon and Comedy Central networks boosted the amount of ad time they aired in the first half of 2012 by 9% from a year earlier, to a combined 1,901 hours. That followed a 7% rise in all of 2011 and a 4% rise in 2010, Nielsen found.