Proving there are plenty of ways to make money via the App Store, virtual currency monetisation company Offpal recently released a case study showing how it had helped Side Hobby's gpsAssassin to switch from a $5 price to free.

The trick is Offerpal handles deals with advertisers and the like, offering gamers free trials, surveys and discount deals for products and, in return, providing them with in-game currency for their trouble.

Indeed, since integrating the system, it claims around 30 percent of gpsAssassin's revenues are now being generated in this manner.

We pinned down Matt McAllister, Offerpal's director of marketing, to find out more.

Pocket Gamer: Can you give us an overview of how Offerpal's virtual currency monetisation system works?

Matt McAllister: When a user is engaged in a game on the iPhone, they might want to get access to a digital good or a premium item that is not available for free. This could be a gift for a friend, a faster engine in a racing game, or, as in the case of gpsAssassin, better weapons or armour to help in a virtual fight.

In gpsAssassin, the virtual currency is Blood Money, so the user clicks on the Earn Blood Money button and browses through our thousands of ad offers such as Netflix subscriptions, surveys, mobile ringtones, and more. When they complete an offer, they're given a certain amount of Blood Money and can then go spend it within the game.

How do developers hook into the system and what flexibility do they have?

For iPhone developers, they hook into the game through the Tapjoy SDK. We give them complete control over the offers by allowing them to choose to either include or exclude certain categories of offers or individual offers themselves.

Can you explain how the gpsAssassin deal came about?

I believe gpsAssassin was already using the Tapjoy SDK, and learned about Offerpal's virtual currency monetisation platform through this.

Are you surprised Offerpal is generating 30 percent of its revenue?

Not at all. In fact we expect to see that percentage grow over time. For games on other platforms like Facebook, offers tend to make up more like 80 to 90 percent of total revenues.

Why do you think gamers are happy to get involved with these offers?

They get hooked on these games, and are happy to shell out a small amount - maybe just a few bucks - in order to get access to certain digital goods or premium items.

But they're even more happy to fork over a few minutes of their time in order to earn virtual currency for free. We're tapping into their strong loyalty to the game itself.

Do you think your system could ever get saturated in terms of there being more demand from consumers than supply from advertisers?

Probably not. We're adding new offers into our system at a rate of 50 - 100 every day, and auditioning offers to see how well they work.

Therefore users - even the addicts who come back every day - can find fresh new offers to take. And we're just hitting the tip of the iceberg in terms of advertisers starting to pay attention to this channel.

Do you have any other high profile iPhone clients?

Yes, TapDefense also uses us. We have several others that we'll be announcing shortly.

Thanks to Matt for his time.

You can find out more details about Offerpal via its website.