According to The Comichron, direct market sales figures pointed to a year-on-year deficit of 11.21% in May.
The downturn was attributed to retailers ordering more Free Comic Book Day titles than profitable books, and this summer's major comic conventions taking place later than usual.
Marvel Comics claimed the bestselling issue of the month with Fear Itself #2, followed by DC's Flashpoint #1 in second place. Avatar Press took top spot in the graphic novel chart with Crossed 3D Volume 1.
Last month, it was reported that the debut issue of Fear Itself gave comic sales in 2011 a much-needed boost, shifting 128,595 copies.
Bestselling comics over the last year consistently sold fewer than 100,000 copies until the conclusion of Jonathan Hickman's Fantastic Four and its rebranding as FF.