Mobile game revenue is expected to nearly double by 2015, Juniper Research predicted today.

According to the market researcher, mobile game revenue topped $6 billion last year. By 2015, Juniper predicts, that figure will be over $11 billion. However, the research firm noted that as time goes on, a shift will occur with revenue migrating from the "traditional pay-per-download model" to in-game purchases.

Juniper expects that by 2013, more revenue will be generated from in-game purchases than from actual downloads of mobile games. The research firm said "discoverability remains a problem for developers and publishers on some app stores," so offering a free title and then getting people to pay for more levels or virtual goods is becoming the more desired way to attract gamers and revenue.

It could be a smart move. Earlier this month, research firm In-Stat reported that virtual goods revenue is expected to reach $7.3 billion this year. In 2007, consumers spent just $2.1 billion on virtual goods. By 2014, the firm predicts, customers could spend more than $14 billion on in-game virtual goods. Although those figures include data from social-networking titles, in addition to mobile games, it effectively highlights the growth in this area.

Juniper also reported that although games are available on several different mobile platforms, "Apple's iPhone/App Store combination has set the benchmark, with a higher share of revenue for developers."