It's always been something of a mystery to figure out how much money is made through revenues of online gaming. Today the NPD Group gave us at least a ballpark figure for that amount with a new report that claims $1 billion in revenue was recorded for online gaming between March 2007 and March 2008. The figure not only includes revenue from PC massively multiplayer game subscriptions but also revenue from console games and from casual game downloads.

The study also listed the top five MMO games in terms of their online subscription revenues and its not a surprise to see Blizzard's World of Warcraft on top. The free web based MMO Runescape was second followed by Turbine's Lord of the Rings Online, Square Enix's Final Fantays XI and NCsoft's City of Heroes. The study also had the top five gaming web sites in terms of paid subscribers and as one might expect casual game sites dominated this segment. Electronic Arts' casual games site Pogo.com was first, followed by Realarcade.com, Bigfishgames.com, Gametap.com and Disney.com.

It's currently unknown if the survey also tracked services like Valve's Steam game downloads. The full report is, of course, available for purchase at NPD's web site.