Books have remained one of the few places without advertising. But not for long.

The market for digital books is $966 million this year and is expected to grow, reports the WSJ.

One digital-book store, Wowio Inc. is selling books with three full page ads - an introduction and a closing page each with an ad, plus another full-page ad. It is also experimenting with ways to inserts ads between chapters.

Wowio charges advertisers between $1 and $3 for each book downloaded and shares revenue with the publisher. The publisher determines how much of those ad dollars trickle down to the author.

Marketers have tried advertising in print books in the past, but it has never generated much revenue. Stuart Applebaum from Random House told the WSJ that ads appeared in the backs of mass-market paperbacks in the 1950s and early '60s, but the practice was abandoned because authors objected.

Imagine an ad for a sports drink that says "Is your day feeling like the worst of times?" that appears in "A Tale of Two Cities" next to the line "It was the best of times, it was the worst of times," or ads for condoms interspersed through "The Scarlet Letter," says Forrester analyst James McQuivey.

Inserting ads in Random House e-books likewise won't happen without author approval, said Applebaum.

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