The more information you can get your hands on, the more honest the industry becomes; so kudos to Brian Robbins, founder of Gravity Sling developer Riptide for providing a detailed breakdown of the early performance of its freemium iPhone game.

Gravity Sling was released with 15 levels, plus another 30 available for 99c as an in-app purchase (IAP) on 5th November.

To-date, it's been most successful on the Japanese and Italian App Stores - reaching #3 in their free games chart, but US market has been more encouraging in terms of the rate of IAP conversion.

The basic rate has been 1.9 percent. This is based on 66,346 downloads (up to 22nd November) and 1,267 IAP sales.



Significantly though, US gamers bought the extra content at a rate of 3.0 percent, compared to the Japanese at 1.9 percent and the Italians at a lowly 0.78 percent.

Another comparison point is those gamers who are signed up to the OpenFeint social network.

In terms of total players, 55 percent had submitted a score via OpenFeint, and this number related to 73 percent of all IAP purchases.

Globally, 3.4 percent of OpenFeint users purchased extra content.



Head over to Riptide's blog to get extra details and graphs, as well as future updates on the IAP rates.