But many other companies are using cost-per-action ads in different ways. “We think it is a model that all the large players in search will be embracing over time,” said Tom McGovern, the chief executive of Snap.

For the time being, Google is not putting cost-per-action ads next to search results, limiting them to publishers’ Web sites and essentially creating its own affiliate marketing network. Industry insiders said Google’s entry into the market was likely to accelerate its growth.

“This is a big market at an early stage,” said Ellen Siminoff, chief executive of Efficient Frontier, a search marketing firm.

Cost-per-action ads have another advantage: They virtually eliminate the problem of click fraud, a scam in which people or computers generate clicks on ads for the sole purpose of getting a payment.