Bowker finds that 148,424 print books were self-published in 2011 — that means that 43 percent of all print books published in the U.S. in 2011 were self-published. 87,201 ebooks were self-published. Publishers Lunch notes a few important caveats: Bowker only counts titles with ISBNs, so “KDP exclusives and other sources that still don’t use ISBN numbers” aren’t included. That means the number of self-published ebooks is likely much higher than 87,201. In addition, the print and digital editions of a single title may be counted twice.

Bowker finds that four large companies dominate the self-publishing space. In 2011, Amazon’s CreateSpace was behind the creation of 58,412 titles, or 39 percent of all self-published print books.

Smashwords was the largest ebook producer, accounting for 40,608 titles, or 47 percent of all self-published ebooks.

Author Solutions, which Penguin acquired earlier this year, and Lulu accounted for 47,094 titles and 38,005 titles, respectively. Author Solutions and Lulu allow customers to self-publish both print and ebooks.

“Beyond those four players, no company has more than 10 percent of market share,” Bowker reports. The company found that small presses, which it defines as publishers who have produced 10 or fewer books, produced 34,107 self-published titles in 2011. The number of print books produced by small presses “increased more than 74 percent between 2006 and 2011″ but that figure is “dwarfed by CreateSpace’s 1702 percent increase during the same period.”

Photo courtesy of Shutterstock user Carlos Andre Santos