Investment banks earned more in fees from just four buyout firms during the peak of the buyout boom than they did from all private equity firms combined over the past 12 months.

Global fee revenues paid to banks by private equity firms The Blackstone Group ($906m), Kohlberg Kravis Roberts ($710m), Apollo Advisors ($572m) and Goldman Sachs Capital Partners ($556m) totalled $2.74bn (€1.88bn) in the 12 months beginning July 1, 2006, according to research group Dealogic. That period, famously called the "golden age of private equity" by KKR founder Henry Kravis, is regarded as the peak of the private equity boom.