http://thewertzone.blogspot.co.uk/2015/03/the-updated-sff-all-time-sales-list.html

The first 20 authors by sales volume are:

1) J.K Rowling (c. 450 million)

2) Stephen King (c. 350 million)

3) JRR Tolkien (c. 300 million)

[Dean Koontz (c. 200 million)]

[Michael Crichton (c. 200 million)]

4) Anne Rice (136 million)

5) CS Lewis (120 million+)

6) Stephanie Meyer (116 million)

7) Edgar Rice Burroughs (100 million+)

8) Sir Arthur C. Clarke (100 million+)

9) Suzanne Collins (100 million+)

10) Andre Norton (90 million+)

11) Sir Terry Pratchett (85 million+)

12) Robert Jordan (80 million+)

[John Saul (60 million+)]

13) James Herbert (54 million+)

14) Terry Brooks (50 million+)

15) Richard Adams (50 million+)

[Dennis Wheatley (50 million)]

[Jean M. Auel (45 million+)]

16) George R.R. Martin (44.4 million+)

[Morgan Llywelyn (40 million)]

17) Neil Gaiman (40 million+ )

18) Rick Riordan (40 million+)

19) Christopher Paolini (39 million)

20) Charlaine Harris (35 million)

Werthead goes into much more detail on his own list, not least about the storming success of GRRM since it was last compiled.

This makes our older thread on the subject somewhat redundant, so I'll close that.