Sales of standalone e-readers might be declining, but ebooks make up a growing portion of sales for US book publishers, according to the latest stats from the Association of American Publishers (AAP), a trade association.

The AAP's annual "StatShot" report for 2012, released on Thursday, shows ebook sales accounting for 22.55 per cent of all revenue for US trade publishers – meaning the typical commercial publishers whose books you find in shops.

That's up from 16.98 per cent in 2011 – a significant increase. And it's a massive step up from just six years earlier, when publishers reported that only 0.5 per cent of their revenue came from ebooks.

The report cautions that book categories and the ways in which publishers report data about ebooks have evolved dramatically over the 10 years that the AAP has tracked the statistics, so strict historical trends are hard to pin down accurately.

Still, the fact that nearly one of four books sold last year was an ebook is a definite eye-opener, as is the fact that ebook publishing is now a $1.54bn business.

The AAP bases its figures on a survey of around 1,200 publishers, which it conducts every month. It compiles annual data each year in December.

The report further notes that ebook sales grew in the adult fiction, adult nonfiction, children's/young-adult, and religious book categories, as compared to 2011 – which is to say, ebooks sales were up in every category that comprises the trade publishing sector.

Publishers shouldn't pop the champagne yet, however. Although the growth in ebook sales in 2012 is encouraging, it's a far cry from the triple-digit growth of previous years, which suggests that sales may be starting to plateau.

Still, the numbers clearly indicate that more Americans prefer to do their reading on an electronic device than ever before. And while that's doubtless encouraging for Amazon, Apple, Barnes & Noble, Google, and other operators of online ebook markets, it should come as sobering news for the proprietor of your local bookstore. ®