CBS Corp., owner of the most-watched television network, reported an unexpected first-quarter loss as advertisers cut spending during the recession.

The loss of $55.3 million, or 8 cents a share, compared with profit of $244.3 million, or 36 cents, a year ago, New York-based CBS said. Sales fell 14 percent to $3.16 billion from $3.65 billion, missing the $3.26 billion analyst estimate.

CBS, controlled by Sumner Redstone, generates 70 percent of its revenue from advertising, the most of any major US media company, and stands to benefit more if ad sales are stabilizing.

CBS fell 56 cents to $7.50 in extended trading. It rose 8 cents to $8.06 in New York Stock Exchange composite trading and has declined 1.6 percent this year.