Search engine and software giant Google holds the biggest chunk of the mobile ad sales market, but according to market research company eMarketer, Facebook may not be too far behind. Between them, the two companies raked in two-thirds of all mobile ad sales in 2013.

Last year was a strong one for mobile ad spending, surging 105% ahead of 2012, but this year is forecasted to surpass that by another 75% in total. According to eMarketer’s predictions, mobile ad sales may add up to a whopping $31.45 billion this year.

In 2011, Facebook only received 11% of its ad revenue from mobile, but that figure rose to around 45% last year, and is expected to continue climbing this year. Facebook has made more of an effort to increase its ad revenue on mobile devices, and the effort appears to be paying off for the world’s largest social network. As more and more of the world’s population makes the move towards mobile technology, advertising opportunities are only expected to rise.