-By Kenneth Hein

Casual gamers in the middle of a hot and heavy game of Word Challenge will have to wait for a word from the sponsor before they can continue. A 15-second spot from Esurance rolls while the gamer waits and then play resumes.

This is just one of the scenarios Google is presenting to marketers as part of its expanded AdSense for Games beta test. Google's in-game advertising network for video, text and display ads launched on a limited basis last November, however beginning today the search  giant is formally inviting marketers and game publishers to jump onboard.

This step forward is an important one for the in-game advertising industry, said Shar VanBoskirk, analyst for Forrester Research, Cambridge, Mass. "It's been kind of an untapped medium for years. It hasn't caught on with as much intensity as people thought it would. This might counter that."

U.S. in-game advertising is currently at the $360 million mark, per Forrester. It was projected to hit $865 million by 2012. However, VanBoskirk said she would consider upping her forecast based on the announcement given Google's history for simplifying interactive ad buys. "It provides an easier way to leverage an underutilized channel," she said.

In a 90-second teaser spot at Google's AdSense blog, the in-game network is touted as the "No. 1 emerging media" reaching a "wide ranging audience" that comprise "billions of minutes of play per month." It also cites comScore data stating that 25% of Web users play online games every week, representing more than 200 million users.

“We see this as adding more tools to the advertiser tool kit,” said Google rep Daniel Rubin. “It extends Google's cross-platform branding solution and gives game developers the ability to monetize their online games, which we hope will fuel the development of high quality gaming content--a good thing for users.”

While Google's entrance took longer than expected (it purchased Adscape in February 2007 for $23 million to offer such an opportunity to marketers), it is still "a significant development," said Paul Verna, senior analyst at eMarketer, New York. "There's every reason to be optimistic that this will only be good for the online game advertising industry."

Casual computer games are more natural place for advertisers than say Microsoft's Xbox 360 or Nintendo's Wii. They reach a wider audience and given that they are free, "most surveys say players are willing to accept some level of advertising," said Verna.

Casual games typically last about six minutes and "aren't as deeply immersive as traditional console games where you wouldn't want to interrupt them," said Verna. Plus "the audience is very addicted."

However, Verna cautions Google AdSense for Games won't become an overnight sensation given the economy and potential growing pains. eMarketer projects in-game ad spending to hit $650 million by 2012. Google's chief competitors already offer similar technologies. Microsoft bought Massive in 2006 while Yahoo! also offers ad-supported games.