Her trilogy has held the top three places in the best-seller lists for seven weeks and the first book in the series, Fifty Shades Of Grey, is already the fastest-selling book of the year.
James's debut shattered the record for weekly sales. shifting 205,130 copies in just seven days. The previous high was 141,000.
New figures show the paperback version has now sold 765,000 copies in two months, a figure which the biggest selling paperback of all time, Dan Brown's The Da Vinci Code, took six months to achieve.
Mother-of-two and former TV executive James, real name Erika Leonard, has already seen the movie rights to her books snapped up.
Industry experts are expecting the paperback Fifty Shades Of Grey to break through a million sales within a month. The trilogy is completed by follow-ups Fifty Shades Darker and Fifty Shades Freed.
Charlotte Bush, publicity director for the books' publisher Arrow Books, said: "The sales figures are phenomenal and we look forward to seeing them grow over the summer - what could be more perfect than relaxing by the pool with a copy of Fifty Shades Of Grey?"
Philip Stone, charts editor of trade magazine The Bookseller, said: "Sales of the Fifty Shades series have been nothing short of phenomenal and records are tumbling. Perhaps most remarkably, the paperback edition of Fifty Shades Of Grey has sold in just two months what Brown's The Da Vinci Code, the best-selling paperback novel of all time, took over six months to achieve.
"It is no doubt breaking ebook download records too, meaning Fifty Shades Of Grey is perhaps the fastest-selling adult novel of all time."
Have you read it yet? What were your thoughts??