LOS ANGELES, Aug. 17 (Xinhua) -- U.S. television network NBC said Sunday that its Beijing Olympics coverage overnight has attracted the highest numbers of viewer on any Saturday night since 1990, as almost 40 million Americans watched Michael Phelps win his unprecedented eighth gold medal.

The Saturday night telecast on NBC averaged 31.1 million viewers, up 38 percent compared to the 22.5 million viewers for the second Saturday during the Athens games in 2004, according to Nielsen Media Research.

NBC said that the network had an audience that size last time on a Saturday night was on Feb. 24, 1990, when 31.4 million viewers watched an "Empty Nest" TV sitcom episode.

At the nine-day mark of the games, NBC said its Olympic coverage has attracted a total of 191 million viewers for its various television channels, including USA, NBCU and Telemundo.

Saturday's ratings peak came when 39.9 million Americans were watching Phelps and the U.S. team win the 400-meter medley relay. By winning his eighth gold medals in Beijing, Phelps surpassed Mark Spitz's record of winning seven gold medals in swimming at an Olympics.