Private equity firms have more than tripled their average returns from emerging market buyouts, which now account for at least a fifth of all deals.

Emerging market deals produced an average internal rate of return - a measure of annual performance - of 17.3% after fees between 2000 and 2006, up from just 5.3% in the 1990s, according to a study published by the IESE Business School and the Boston Consulting Group.