EBay will start running advertisements on its mobile app during the fourth quarter, moving the e-commerce company into the fast-growing market for ads on devices like tablets and smartphones.

Users spend 150 minutes on its app per month, three times higher than its nearest rival, said Stephen Howard-Sarin, eBay's head of display advertising in North America.

The company can tailor its ads because users have single, universal login across their devices, Howard-Sarin said.

Berkshire Hathaway's insurance unit Geico is among the first advertisers on the company's mobile ad network, according to Reuters.

Mobile ad spending in the United States is expected to reach $17.73 billion this year. This is an increase of 83 percent from $9.69 billion in 2013, according to industry research firm eMarketer.

Though advertising is a higher margin business than retail, but the move risks turning people away from eBay's website.

Howard-Sarin isn't worried about the risk, saying that many users repeatedly return to the site.

He believes that the site's relationship with users "can survive a blip or two," according to Reuters.

"If they respond to (the mobile advertising), we're not so brittle that we think that's going to destroy their relationship with eBay," Howard-Sarin said. "They're going to come back as soon as they're done and we're not afraid of that."

EBay is working with Triad Retail Media to place the advertisements.

Howard-Sarin declined to provide details of the revenue sharing agreement. It said it will get a greater portion of the revenue, according to Reuters.

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