Research firm eMarketer expects spending on mobile advertisements to hit nearly $9.6 billion in the U.S. this year, up from $4.4 billion in 2012 and from less than $1.6 billion in 2011.

Mobile ads now represent nearly 23 percent of the money companies spend on digital advertising, or ads people see on their computers, tablets and mobile phones. That’s up from about 12 percent last year and less than 5 percent in 2011.