The fees fund managers charge big institutional clients, such as pension funds, are falling steadily, but in-demand private equity firms are bucking the trend, according to a new study.

The decline in charges is saving large investors tens of thousands of dollars a year, the report from the investment consultancy Bfinance found. It also illustrates the impact on fund managers’ revenues, with companies under pressure to slash their prices as investors flock to much-cheaper index funds.