Google is the sleeping giant when it comes to advertising in video games. While the company dominates search advertising, it has yet to make a big splash in video games. That could change soon, as the company has been quietly testing its “AdSense for Games” product for months.

Sources close to the matter said that the company has developed an in-game advertising technology that allows it to insert video ads into games. In demos of the technology, a game character can introduce a video ad, saying something like, “And now, a word from our sponsor,” before showing a short video at the end of a sequence in a game. Since testing has been going on for some time, Google could launch the technology fairly quickly, if it so chooses.

But it’s not clear why Google hasn’t already launched its in-game advertising business, given that the seeds of AdSense for Games were planted in early 2007. Google did not respond to a request for comment this morning. I’ll update if that changes.

“I don’t know what’s taking them so long,” said one source close to the matter. “They could move into this market very quickly, given what they have shown off.”

If the company enters the market, it should stir up the competition the way it has in other ad markets. Companies such as Double Fusion, IGA Worldwide, Microsoft’s Massive, MochiMedia and NeoEdge Networks have been carving out niches with in-game or wrap-around ads for some time.