A new study published last month claims revenue from the sale of digital content in games like Mafia Wars and Battlefield Heroes will be over $1 billion by the end of 2009. Top reasons for the surge (more than double last year’s record) include an expanding population of casual gamers and the increasing sophistication of casual games on platforms like Facebook.

According to a recent Financial Times article, financial analysts Justin Smith and Charles Hudson monitored the sale of virtual goods across gaming platforms like Facebook, Second Life, Xbox Live and the iPhone App Store. “I don’t know anyone who expected it to grow this fast,” said Smith in an interview with GamesBeat. “The Facebook platform went from zero to hundreds of millions of dollars in two and a half years. It reflects a broader shift in society where people are spending more time on casual games.”