Young readers, from children to young adults, have made e-books the fastest growing area in book sales, US industry figures show.
The Association of American Publishers said 22.6 million children's and young adults e-books were sold in January, compared to 3.9 million sold in January a year ago.
Older readers are taking to e-books as well, pushing sales up from 66.6 million e-books sold in January 2011 to 99.5 million sold in January 2012.
Adult e-books are set to overtake adult paperbacks as the highest-volume product for publishers in America.
Paperbacks outsold e-books by fewer than 6 million units in January, with projected e-book sales growth certain to make e-books the number-one category for U.S. publishers, venturebeat.com reported Friday.
The rise in e-book sales is being driven by the surge in e-readers and tablets, with tablet ownership doubling during the holidays, venturebeat.com said.