Online game publisher Shockwave.com, a division of AtomShockwave, will begin offering advertisers a way to insert ads within casual web-based games - which attracted nearly 56 million unique visitors to various sites in September, according to comScore - the Associated Press reports. Shockwave.com hosts more than 200 games and claims that its 20 million visitors last month played more than 25 million game sessions.

Shockwave's ad network, launched today, will allow marketers to insert images or brand names in the games, track impressions or viewing times for each ad, and tailor ads to geographic markets.

SBC, Sprint Nextel and Sony Pictures are among the first to use the new system. The ad insertions will begin with action games in which the landscape allows billboard-like advertisements. Ad images will generally last 3-7 seconds in those games

The may last longer in games where an ad can be displayed on the hood of a car, for example, said Dave Williams, chief marketing officer of AtomShockwave. The company plans to introduce ads in mind and puzzle games, too, but only if they can be incorporated into the design without interfering with game play, according to Williams.