More than $966 million of e-books will be sold in the US alone this year, according to a new Forrester report.
The firm predicts that this will nearly triple to just under $3 billion by 2015 - a target described by Forrester analyst James McQuivey as "easy to hit".
According to the report, only seven per cent of online adults who read books read e-books, but they tend to be the people reading most, and spending most on books.
"Here’s the kicker – the average e-book reader already consumes 41 per cent of books in digital form," McQuivey wrote in a blog post.
"Oh, and that includes the people who don’t have an eReader yet, which is nearly half of them. For those that have a Kindle or other e-reader, they read 66 per cent of their books digitally."
Forrester describes the predictions as an important wake-up call for any elements of the traditional publishing industry who are still dragging their heels on digitisation.
"In the book business, it means that traditional publishers can no longer live in deny-and-delay mode," he wrote.
"Not only do publishers need to take digital seriously, they must make it the new default for publishing, preparing for a day in which physical book publishing is an adjunct activity that supports the digital publishing business."
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