The adult coloring book craze that started at the beginning of 2015 shows no sign of slowing down. Lost Ocean, Johanna Basford’s newest book (and her first published by Penguin), sold more than 55,000 copies in the first week after its October 27 release, according to Nielsen BookScan. Her first two books were published by Laurence King: Secret Garden and Enchanted Forest have sold more than 453,000 copies and 350,000 copies, respectively, so far this year.

Since adult coloring books don’t have their own BISAC code, they appear in different categories in BookScan, but most titles are grouped under art, and coloring books dominate that list (Basford’s books appear on the juvenile nonfiction list). A list of some of the biggest sellers to date shows that 10 of the most popular books have combined to sell about 1.5 million copies at outlets that report to BookScan, which captures about 80% of print book sales. And many publishers note that they have done very well in nontraditional outlets that do not report to BookScan