Bertelsmann's Random House, the world's biggest book publisher, expects electronic books to contribute more than 10 percent of its U.S. revenue next year, its head was quoted as saying on Sunday.

Random House chief executive Markus Dohle told German magazine Der Spiegel that e-book revenue had already jumped to 8 per cent in the United States and had turned into a new growth driver for the publisher of Dan Brown, John Grisham and Stieg Larsson.

'We're at eight per cent in the United States currently, it rose by leaps and bounds,' Dohle told Der Spiegel. 'I could well imagine that we get beyond 10 per cent next year,' he said. 'This is a major opportunity for us. It helps us record new growth.'

Amazon.com Inc's Kindle, the newest version of which launched last week, and Apple Inc's iPad tablet computer have created a fast-growing mass market for e-books, which at Amazon already outsell printed books.

Dohle said that he did not expect e-books to generally overtake printed books in the next five years, however.

'I don't share this view, that's too aggressive, too much hype for my taste,' he said. 'The share will probably be somewhere between 25 and 50 per cent by 2015, even in the United States.'

Random House is so far not offering its books on Apple's iPad because Dohle said he was not sure about Apple's model which forces publishers to determine the end-consumer price, unlike for printed books which are priced by retailers.

'We've got to think very hard about whether we want this drastic change in our business model,' he said. 'The question is if publishers know how to find the right retail price. This hasn't been our job in the past.'

'One hundred days in the iBook store won't decide about success or failure,' he said. 'We think we have to tread carefully to find a business model that is sustainable for the years to come.'-Reuters