Managers at a typical private equity firm or hedge fund collect from their investors management fees based on the size of the fund. But most of their compensation comes as a share of the profits earned by the fund. The Internal Revenue Service allows those profits to be considered “carried interest,” taxed at the capital gains rate typically reserved for investments.

The tax strategy used by Bain and other firms to convert management fees — the compensation normally taxed as ordinary income — into capital gains is known as a “management fee waiver.” The strategy is widely used within the industry: 40 percent of the 35 buyout firms based in the United States surveyed in 2009 by Dow Jones said their partners used at least some of the firm’s fees to make investments in their funds.

But some prominent firms appear to avoid the practice. The Carlyle Group and Blackstone Group have stated in regulatory filings that their partners have not diverted management fees into investments in their funds.

In the varied world of private equity, some firms may have lawyers who are not aware of the strategy or have steered their clients away from it, said a lawyer at one firm who has used the strategy for his clients. Others, he said, may not have the operational capabilities to handle the complex transactions.

Apollo Global Management, the buyout firm co-founded by Leon Black and now publicly traded, is among those that use the conversion strategy. Between 2007 and 2011, Apollo converted more than $131 million in fees into investments in its funds, according to S.E.C. filings. A spokesman for the firm declined to comment.

Likewise, K.K.R. converted more than $180 million in fees between 2007 and 2009, according to its filings. Kristi Huller, a spokeswoman for the firm, declined to comment about any regulatory matter, but said in an e-mail that K.K.R. had not used the tax strategy “for the past few years.”