More ads hit online TV as Web audiences grow.

One of the rewards of watching TV online is not having to sit through as many commercials. Now the networks are chipping away at that little luxury. CBS shows twice as many ads per show on its website as it did last year. The CW network shows four times as many. Dozens of shows from major cable networks now carry as many ads online as they do on TV. More shows will follow soon.

The online audience is still small compared with television, but it's growing. Networks hope that by showing more ads, they can make about as much money per viewer online as they do on the tube.

It's a change from the early days of online video. When ABC started putting full episodes of its shows online in 2006, fans could zip through the hour-long dramas "Lost" and "Desperate Housewives" in about 45 minutes. One short ad played a few times per show. Limiting commercials kept people from going to unauthorized websites to watch pirated copies of shows. It also helped networks reach new audiences in college dorms and teenage bedrooms.