Amazon Underground, a portal offering free Android apps, is now available in 16 more markets in Europe, including Italy and Spain.

However, some of the new additions – such as Gibraltar, Isle of Man, Liechtenstein, Andora, Vatican City and San Marino – are unlikely to make developers rich.

Amazon Underground was previously available in US, UK, Germany and France.

Since any developer can submit an app to the store, Amazon said more apps and games will be added to the Underground catalogue all the time.

The platform offers a unique monetisation model. Developers waive their download and in-app fees in exchange for being paid by Amazon every minute their app is used by every customer.

“You can monetise 100 per cent of your Android user base and maximise downloads, since everything is free for users,” the company said.

Rovio, the developer of Angry Birds which recently experienced job cuts, said  it saw revenues triple since launching four games on the service.

According to SVP of game business, Tero Raji, “in the first month since launch of these games, the Amazon Underground model has brought us up to three times more revenue compared to the same games’ user revenue in the Amazon app store previously.”

Amazon believes its model lets developers focus less on monetising their product and more on user experiences that keep customers engaged for long periods of time.

The Amazon Underground app is available for download on Android phones and BlackBerry 10 devices, and is preloaded on Fire tablets.