Facebook is positioned to become the number-two seller of digital ads in the U.S. and worldwide for the first time. Mobile growth has been the primary contributing factor to the social network’s rise in position — which had previously been fourth place. Now, Facebook is between Google, at number one, and Microsoft, at number three. Mobile advertising was just three percent of global digital ad revenue in 2010 and has shot up to 22 percent since.

According to VentureBeat, the forecast, by market research firm eMarketer, said Facebook contributed $9.6 billion in revenue to the online ad sector in mobile ads alone. “The advance of mobile use, with its rich ecosystem of applications and an increasing inventory of devices, has turned this once negligible slice of the ad market into a major factor,” explains the article.

Instagram, which was acquired by Facebook last year, is also releasing results of the first six weeks of advertising on the photo-sharing platform. The initial ad campaigns included 10 advertisers. Among the findings, there was a “32 percent incremental lift in ad recall per campaign for people who were repeatedly exposed to a particular campaign versus control groups,” according to Mashable.

“There was also a 10 percent incremental lift in brand message awareness per campaign for people who saw an ad or ads compared to those who didn’t,” the article adds. Levi’s and Ben & Jerry’s, for example, reached 7.4 million people and 9.8 million people respectively within timeframes of eight and nine days. Compared with their follower counts, they reached audiences 47 and 29 times bigger than usual.

Mashable reports a Facebook ad partner cautioned that one reason the Instagram campaigns worked is that Facebook “kept meticulous control of the quality of the ads.” That will be more challenging to maintain when the number of advertisers grows significantly.

“According to eMarketer, Facebook will take 7.4 percent of American digital advertising for a total of $3.17 billion this year, with Google capturing about a fourth of the market, for $17 billion in income,” notes VentureBeat. “Facebook will gain the #2 position globally as well as nationally, taking 5.64 percent of the worldwide market to Google’s 31.91 percent.”