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A new report by BookStats finds that trade (consumer) ebook revenue in the U.S. was roughly flat between 2012 and 2013, even as the number of ebooks sold rose by 10.1 percent to an estimated 512.70 million.

With more ebooks being sold, the seemingly contradictory 0.7 percent drop in revenue suggests they’re being sold at lower prices.

BookStats also estimates that book publishers now make more revenue from online sales (of both print and digital books) than from brick-and-mortar stores, with $7.54 billion coming from online sales and $7.12 billion coming from physical stores in 2013.

What about self-published ebooks? BookStats includes “any self-published book registered with a US commercial book identifier number (an ISBN)” in “the extrapolation and methodology of the report” but ebooks without ISBN numbers — which includes many self-published Kindle books — can’t be tracked. BookStats also cautions that “the report only captures publishers’ net revenues, not retailer/consumer sales.”

BookStats, which is a joint project between the Association of American Publishers and the Book Industry Study Group, collects data from more than 1,600 publishers to create its estimates. The BookStats “trade” (or consumer) category includes adult fiction and nonfiction, children’s/YA and religious books. Full reports can be ordered here.

Photo courtesy of Shutterstock/Enzode Bernardo

This post was updated Thursday afternoon with some information about self-published ebooks, and I also changed the headline to better reflect the fact that the chart focuses on U.S. publishers’ ebook revenues, not on the size of the ebook market as a whole.