Mobile is not only booming, it’s also growing faster than all other digital advertising formats in the U.S. now that advertisers are allocating more dollars to catch the eyes of a growing class of “mobile-first” users.

According to BI Intelligence, there was once a big disparity between the amount of time people actually spent on their smartphones and tablets (significant and growing), and the amount of ad money spent on the medium (still small).

Now the research outfit expects that this gap will narrow substantially, as enthusiasm grows for mobile-optimized ad formats (such as interactive rich media and native ads), as targeting improves, and as more and more advertisers grok how to effectively leverage the platform.

“New data from BI Intelligence finds that US mobile ad spend will top nearly $42 billion in 2018, rising by a five-year compound annual growth rate (CAGR) of 43 percent from 2013,” according to Business Insider. “Its report looks at the most important mobile ad formats, including display, video, social, and search. The report provides exclusive breakdowns on how spend on each format will grow and why, and examines the overall performance of mobile ads. It also looks at how programmatic ad-buying tools, including real-time bidding, are reshaping mobile advertising.”