A confidential, seven-page Google Inc. “vision statement” shows the information-age giant in a deep round of soul-searching over a basic question: How far should it go in profiting from its crown jewels—the vast trove of data it possesses about people’s activities?

Should it tap more of what it knows about Gmail users? Should it build a vast “trading platform” for buying and selling Web data? Should it let people pay to not see any ads at all?

The vision statement describes the company’s immense search database as “the BEST source of user interests found on the Internet,” during a discussion of ways to make ads more relevant to users. “No other player could compete,” it says. Later, the document warns that some ideas range from “safe” to “not” safe.

The most aggressive ideas would put Google at the cutting edge of the business of tracking people online to profit from their actions. A data-trading marketplace, for instance, would allow personal information from many sources—including Google—to be combined and used for highly personalized tracking of individuals. Tiny companies like BlueKai Inc. and eXelate Media Ltd. already offer some of these services, pressuring Google to match them. A Wall Street Journal investigation, “What They Know,” is examining the widening trade in this kind of data and the consequences for individual privacy.

Google trails in some of these techniques by choice. Famous for its unofficial corporate motto, “Don’t Be Evil,” for years it resisted using any method to track people online without their knowledge at the fierce insistence of founders Sergey Brin and Mr. Page. But the two men have gradually decided they can begin exploiting the data their company controls, without exploiting consumers, according to interviews with more than a dozen current and former employees.