NEW YORK: The heat is on: Sales for E.L. James' ''Fifty Shades'' trilogy are at 10 million and counting, making it among the fastest-selling series of all time.         

The explicit sensation has topped charts practically from the moment Vintage Books released it in early April. Reprints have exceeded 900,000 copies in a single day, the publisher announced Tuesday. Totals sales include paperbacks, e-books and audio books. Vintage is a paperback imprint of Random House Inc.

The ''Fifty Shades'' books began as fan fiction, inspired by the ''Twilight'' series, and were a word-of-mouth hit after first being distributed in 2011 by the Australia-based Writer's Coffee Shop Publishing House. Film rights have been acquired by Universal Pictures and Focus Features.