U.S. TV networks locked in about $8.7 billion in advertising commitments for the season that starts in September, an 8.1 percent increase that would have been bigger without signs of a weakening in the economy.CBS Corp. (CBS), owner of the network with the largest overall audience, commanded the highest rate increase, averaging 13 percent to 15 percent, said a person familiar with the results. Comcast Corp. (CMCSA)’s NBC, Walt Disney Co. (DIS)’s ABC and News Corp.’s Fox raised prices from 9 percent to 11 percent.