There’s a reason companies like Google, Facebook, and now AT&T are working to improve mobile ad experiences for users. And that reason is money, lots of it.

In the first half of 2016, mobile accounted for half of combined advertising revenue from display and search ads in the United States, IHS Markit said.

According to IHS Markit data, mobile’s share of search ads amounted to 46.4 percent – or $3.9 billion – of overall U.S. search revenue totalling $8.4 billion in the first half of the year. Mobile did even better among display ads, raking in 54.8 percent – or $4 billion – of U.S. online display ad revenue totalling $7.3 billion.

Those figures represent mobile search and display growth of 101.4 percent and 71.5 percent year over year, respectively, IHS Markit said.

But the United States isn’t the only market where mobile search revenues are growing. A report from IHS Markit last week indicated mobile advertising in Europe generated just over $4 billion (3.8 billion euros) in the first half of the year, split evenly between search and display ads. Mobile’s share of online search ads overall was 32 percent and its share of online display ads was 32.8 percent, representing growth of around 57 percent and 61 percent, respectively.

“Mobile accounted for one in three euros spent in Europe,” Eleni Marouli, principal analyst at IHS Technology, said. “We expect mobile to play a primary role in European online advertising and to maintain growth at a double-digit level for 2016.”