The latest Lara Croft video game is to be launched on Microsoft’s Xbox console as a series of downloadable “episodes” available over the internet – a first for the world’s biggest software maker.

Underscoring a shift in the games sector towards the online model championed in music by Apple, Microsoft will make Tomb Raider Anniversary available through Xbox Live Marketplace, its online games platform, which boasts more than six million members.

Jane Cavanagh, the chief executive of SCi Entertainment, the developer behind the Lara Croft franchise, said: “This is part of our strategy to grow our presence in online and digital distribution as we believe there are huge growth opportunities.”

The Tomb Raider series is still one of the best selling videogame franchises of all time with over 32 million copies sold and two feature films released, starring Angelina Jolie. Conventional versions of Tomb Raider Anniversary released on disc for Sony’s PlayStation 2 and the PC have led the UK charts this month.

By piping titles directly to consumers and sidestepping traditional retailers, games makers hope that internet distribution will boost margins by stripping out packaging and shipping costs. SCi has suggested that downloading games can increase the returns the group makes on titles by 20 per cent.

The market for digital downloads of video games still only accounts for a sliver of the $30 billion-a-year games market but is growing rapidly.

Microsoft's Xbox Live online gaming network has accrued more than 2.3 billion hours of online gaming – equal to more than over 260,000 years – since its launch in 2004. The platform has downloaded more than 135 million downloads since the launch of Xbox 360 in 2005.

According to ScreenDigests, the analysts, the games download market is expected to exceed $289 million by 2010, with web-based “games on demand” services topping $104 million.

The online versions of Tomb Raider Anniversary will be available in four episodes. Episodes 1 & 2 will be available – with a free downloadable training mission – in September. The next two episodes are due to follow “shortly afterwards”. A full traditional retail version is planned to be released for Xbox 360 later in the year. Each episode will cost about $30 in the US. UK prices were not immediately available.

This year, SCi said that strong sales of Tomb Raider games had helped put the group on course for annual pretax profits of £30 million, up from £23 million a year earlier.

SCi bought Eidos, the Tomb Raider publisher, in 2005, an acquisition that has helped to boost SCi’s revenues sevenfold over the past two years.

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