Amazon CEO Jeff Bezos got a “wake-up” call a decade ago, when he got word of a project at Google to scan and digitize product catalogs. “He saw it as a warning that the Web search engine could encroach upon his online retail empire, according to a former Amazon executive,” reports Reuters. That was just the beginning of a rivalry that will continue heating up in 2013. The two will compete even more fiercely in the online advertising, retail, mobile gadgets and cloud computing realms.

Reuters says these overlaps are representative of a “tech industry war in which many combatants are crowding onto each others’ turf. Lurking in the shadows for both Google and Amazon is Facebook with its own search and advertising ambitions.”

Perhaps the most intense of the battles will be within the online ad space, in which Amazon might actually have a leg up on Google, according to Mark Grether, chief operating officer of Xaxis, an audience buying company.

“From a client’s perspective, the data that Amazon owns is actually better than what Google has,” says Grether. “They know what you just bought, and they also know what you are right now trying to buy.”

According to research from Forrester, “30 percent of U.S. online shoppers in the third quarter began researching their purchase on Amazon.com, compared with 13 percent who started on a search engine such as Google – a reversal from two years earlier when search engines were more popular starting points.”