Advertising marketplace OpenX of Pasadena brought in more than $140 million in revenue last year, the company announced Tuesday.

OpenX’s revenue increased 40 percent year-over-year, the company said, and much of that revenue came from mobile advertising sales, which increased 100 percent year-over-year. The advertising marketplace also added more than 250 publishers last year.

Through its automated marketplace, OpenX earns revenue by facilitating the sale of advertisements on behalf of online publishers. The company has focused on selling advertising inventory for higher quality publishers, a strategy that has helped it maintain higher advertising rates, said Chief Executive Tim Cadogan.

“We turn away 30 to 40 percent of the publishers because we feel they don’t have the right quality,” he said, noting that OpenX examines publisher business models for potential risks. “We are looking at how much traffic you buy. That immediately throws up risk signs.”

The company also looks for fraudulent Internet traffic, which is created by software programs called “bots,” he said.

OpenX’s revenue growth has been especially driven by growth of mobile advertising sales. Though mobile advertising technology doesn’t yet have targeting capabilities that match desktop-based advertising technology, thus keeping down advertising rates, Cadogan said he expects the category to catch up over the next year.

“It’s a significant growth opportunity: You have growth in volume and possible a significant upside in the monetization of mobile as well,” he said.

Revenue growth has also been matched with a growing headcount at OpenX. The company hired 110 employees last year, a 31 percent increase in the firm’s headcount year-over-year.

Technology reporter Garrett Reim can be reached at [email protected]. Follow him on Twitter @garrettreim for the latest in L.A. tech news.