The list below is the top 40 Thoroughbreds on career earnings anywhere in the world from
https://www.thoroughbredracing.com/articles/worlds-all-time-highest-earning-thoroughbred-racehorses/ . All prize money, wherever earned, has been converted to pounds sterling based on the relevant exchange rate at the time.
Their " list was originally compiled by the International Racing Bureau, which is a British company, hence the use of sterling and the official overseas currency exchange rates issued by the British Horseracing Authority in the first week of every January.
In my opinion this is a lazy way to measure earnings. Quite a few European horses travel to the US, Hong Kong or Australia at the end of a calender year and exchanges rates can and do yo-yo over very short periods. The British Horseracing Authority gets a fail and needs to lift it's game. Interestingly there is very little difference between my more recent foreign earnings conversion figures and those now on racing.nsw and racing.com. (eg Hartnell). Some of the early figures for implied exchange rates used by the then racingvic website were very different from the true exchange rate.
I have included my GBP figures for comparison purposes.
Horse thoroughbredracing.com figures My figures
Arrogate (USA) 2013 GBP 13,671,322 GBP 13,877,428
Gentildonna (JPN) 2009 GBP 12,285,608 GBP 11,569,967
Orfevre (JPN) 2008 GBP 12,275,482 GBP 11,880,602
Gun Runner (USA) 2013 GBP 12,260,411 GBP 11,808,858
Kitasan Black (JPN) 2012 GBP 11,454,079 GBP 12,375,699
Winx (AUS) 2011 GBP 10,681,440 GBP 11,109,510
Buena Vista (JPN) 2006 GBP 10,588,889 GBP 12,781,143
T M Opera O (JPN) 1996 GBP 10,587,690 GBP 10,881,316
Gold Ship (JPN) 2009 GBP 9,940,344 GBP 9,433,351
California Chrome (USA) 2011 GBP 9,455,421 GBP 10,104,313
Victoire Pisa (JPN) 2007 GBP 7,959,527 GBP 8,318,408
Vodka (JPN) 2004 (mare) GBP 7,580,245 GBP 8,092,149
Highland Reel (IRE) 2012 GBP 7,513,355 GBP 7,875,927
Espoir City (JPN) 2005 GBP 7,459,286 GBP 7,278,456
Deep Impact (JPN) 2002 GBP 7,268,753 GBP 6,934,759
Hokko Tarumae (JPN) 2009 GBP 7,184,409 GBP 6,820,807
Smart Falcon (JPN) 2005 GBP 6,781,037 GBP 7,227,494
Lord Kanaloa (JPN) 2008 GBP 6,470,184 GBP 6,216,239
Thunder Snow (IRE) 2012 GBP 6,302,421 not reviewed
Enable (GB) 2014 GBP 6,377,396 GBP 6,447,102
Cigar (USA) 1990 GBP 6,277,311 GBP 6,405,361
Flintshire (GB) 2010 GBP 6,240,977 not reviewed
Cirrus des Aigles (FR) 2006 GBP 6,179,490 not reviewed
Vermilion (JPN) 2002 GBP 6,058,055 GBP 6,211,385
Maurice (JPN) 2011 GBP 6,004,693 not reviewed
Treve (FR) 2010 GBP 6,002,918 not reviewed
Viva Pataca (GB) 2002 GBP 5,994,640 not reviewed
Special Week (JPN) 1995 GBP 5,929,086 GBP 5,700,644
Gloria de Campeao (BRZ) 2003 GBP 5,927,616 not reviewed
Narita Brian (JPN) 1991 GBP 5,856,861 GBP 5,949,782
Eishin Flash (JPN) 2007 GBP 5,849,194 GBP 5,845,679
Makybe Diva (GB) 1999 GBP 5,795,064 GBP 6,028,031
Zenno Rob Roy (JPN) 2000 GBP 5,791,478 GBP 5,814,128
Skip Away (USA) 1993 GBP 5,768,753 not reviewed
Just A Way (JPN) 2009 GBP 5,735,667 GBP 5,544,778
American Pharaoh (USA) 2012 GBP 5,531,104 not reviewed
Tap Dance City (USA) 1997 GBP 5,404,241 GBP 5,695,073
Curlin (USA) 2004 GBP 5,291,024 GBP 5,291,580
Dunaden (USA) GBP 5,271,584 not reviewed
Stay Gold (JPN) 1994 GBP 5,261,565 GBP 5,629,967
Some that should be on the list:
So You Think (NZ) 2006 omitted GBP 5,445,105.35
Found (IRE) 2012 omitted GBP 5,525,376.95
Two that suffered due to low rates of exchange against the GBP (and USD):
Sunline (NZ) 1995 less than GBP 5m. GBP 4,343,754
Vengeance of Rain (NZ) 2000 (raced in Australia as Subscribe) less than GBP 5m. GBP 4,786,231