Twitter's global ad revenue is expected to hit nearly $1 billion in 2014, according to a new estimate from eMarketer.

The researcher upped its estimates for Twitter's ad revenue this year and next based on greater-than-expected demand for Twitter's mobile ads. eMarketer now expects that Twitter will generate $583 million in ad revenue in 2013 and $950 million in 2014, up from a previous estimate of $545 million this year and $808 million next year.

"The upward revision comes as advertisers have shown more interest in spending money on mobile advertisements on Twitter, and as recent audience figures from multiple research sources analyzed by eMarketer have suggested Twitter's reach is improving," the report says. eMarketer also attributes some of the increase to the launch of Twitter's API last month.

Mobile ads will account for just more than half (53%) of Twitter's total ad revenue this year and more than 60% by 2015. In fact, Twitter is expected to earn more in mobile ad revenue this year (about $308 million) than it made in total from ad revenue last year.

Even with the revised estimate, eMarketer's estimate still falls short of the projections of some Twitter insiders. Bloomberg reported last year that sources close to Twitter expected the company to do more than $1 billion in ad revenue by 2014.

Image courtesy of Twitter