There are drawbacks to the sector, however, and viewability and fraud top the list. According to the report about half (52%) of advertisers worry about the rate of in-app fraud when it comes to placing ads in the space and nearly half (48%) worry about view ability and measurement challenges associated with mobile and in-app advertising.

"As buyers increasingly embrace programmatic in-app opportunities, transparency and quality are critically important," said Paulina Klimenko, Senior Vice President of Corporate Development & General Manager of Mobile, PubMatic. "Brands are leveraging their buying power to make smarter investments in programmatic, and it is imperative that publishers and ad tech providers alike understand buyers' needs and challenges with regard to in-app environments. By focusing and innovating around data capabilities and inventory quality, supply providers can capitalize on the growing opportunities available in-app."

To gain advertisers' trust, PubMatic suggests that publishers focus on targeting options and quality (73%) as well as the quality of the ad inventory (58%) and brand safety (56%).

Study: Programmatic In-App spend up

Look for more advertisers to add programmatic in-app ads to their digital campaigns. That's the word from new PubMatic data, which indicates that about 25% of digital ad budgets could soon go toward mobile apps.