According to a recent report by the market research firm Gartner, returns from the burgeoning mobile ad market are clearly on the verge of becoming the key source of revenue for app developers in the coming years.

The report says that games will lead in popularity, and shopping and social apps will grow – with the number of downloads from applications stores projected to reach nearly 21.6 billion in 2013, as against the 2009 download figures of 2.5 billion.

Noting that revenue will grow from $4.2 billion in 2009 to $29.5 billion in 2013, Carolina Milanesi, research director at Gartner, said that ad-supported free applications will account for almost 25 percent of application store revenue; vis-à-vis the last year contribution of a mere 5 percent.

Further adding that the ever-growing mobile ad market will probably reach $600 million worldwide this year, Milanesi said that users will become less willing to pay for mobile applications. As such, with money not necessarily coming from end users, developers looking for profitability will have to work towards securing advertising deals.

That mobile advertising will see immense growth in the next few years is also evident from the fact that leading vendors have upped their investments in mobile ads - while Google acquired the Accel-backed AdMob ad network in November, Apple took over Quattro Wireless earlier this month!