By CLAIRE CAIN MILLER

Google’s bread and butter has been search ads — the few lines of text that show up alongside search results that are based on the keywords that people search for. But for some advertisers, especially online retailers, those aren’t necessarily the best type of ads.

On Thursday, Google introduced a new type of ad to all advertisers, called Product Ads. These show pictures of products, along with a short description and price. For the first time on Google, advertisers can pay only if the person buys the product, not just for a click. And instead of bidding on many different keywords using AdWords, Google chooses the searches for which it shows their ad.

The ads make the most sense for e-commerce sites and correspond with Google’s increasing push into comparison shopping on the search engine. Frequent online shoppers and Google users will have noticed that when they search for a product, Google shows images of the product and prices for a variety of sites in the search results.

“If you want to actually buy something, you want to see the price, you want to see the picture of what it looks like,” said Susan Wojcicki, senior vice president overseeing all Google ad products.

Google has been testing the new ads for a year with 800 advertisers, including Campmor.com and Diapers.com

These shopping sites bid on thousands of keywords, but they have even more products. For example, for a single stroller, Diapers.com might need to bid on keywords like stroller, baby gifts, and the brand name. Now, they give their product feed to Google, and Google automatically matches ads to searches.

“You do give up some control in terms of the targeting, but you also gain a lot and eliminate some of the risk of playing in AdWords, where you might get 100 clicks a month and no conversion,” said Michael Manta, marketing manger, Diapers.com. “Here we get 100 clicks but we don’t pay for them.”

During the test period, the new product ads have had twice the click-through rate as text ads for the same thing in the same space, said Jerry Dischler, a Google product manager.

Google has been pushing its comparison shopping offerings and is introducing the new ads just in time for holiday shopping.

“We think it means we’re going to have a much broader range of products in Google,” said Dennis Woodside, vice president of ad sales for the Americas.

The new ads are different than the image ads that Google introduced in July, which show up only when people search Google Images, and are tied to keywords and paid for on a cost-per-click basis like traditional Google search ads.