The private equity firm plowed an additional $16.2 million into the steelmaker, but when the industry experienced a downturn in the late 1990s, the company could not manage its heavy debt. It filed for bankruptcy in 2001, but Bain’s investors still earned at least $9 million.

Debt from acquisitions, usually part of a “roll-up” strategy of buying competitors, played a role in at least five of the seven bankruptcies The Times examined. In most of these cases, Bain investors garnered some initial gains before the companies faltered.

For example, after Bain acquired Ampad, a paper products company, in 1992, the company grew through a series of acquisitions. Sales jumped, but its debt climbed to nearly $400 million, and it found itself squeezed by “big box” office retailers. It filed for bankruptcy in 2000. Bain and its investors walked away with a profit of more than $100 million on their $5 million investment, on top of at least $17 million in fees for Bain itself, according to securities filings and investor prospectuses.

A similar phenomenon unfolded with DDi, a Bain-owned circuit board maker that expanded aggressively in the late 1990s. Sales soared, but so did its debt. The bursting of the tech bubble forced it to scale back. It filed for bankruptcy in 2003. The gains for Bain’s investors easily exceeded $100 million. Bain also collected more than $10 million in fees.

Substantial Fees

The numerous fees collected by private equity firms have been a frequent lightning rod for the industry. First, the firms charge their investors a percentage of the fund as a management fee, meant to cover its overhead. During Mr. Romney’s tenure, this was initially 2.5 percent and then dropped to 2 percent. Private equity firms also collect transaction or deal fees, ostensibly for advisory work, from companies they buy. These fees are generally collected for major transactions, like the purchase of another company, a public stock offering or even the initial acquisition of the company. A third fee stream comes from annual monitoring or advisory fees that portfolio companies typically pay to their owners, the buyout firms.

These fees can be substantial. In the case of Dade International, a medical supply company in which Bain acquired a stake in 1994, Bain and other investment firms piled up nearly $90 million in fees over seven years. The company filed for bankruptcy in 2003 but not before it had borrowed heavily to pay $420 million to Bain and other investors several years earlier.

In 1998 alone, Mr. Romney’s final full year at Bain, The Times was able to identify roughly $90 million in fees collected by the firm across its various funds, a figure that is probably low because most companies in Bain’s portfolio did not have to file financial disclosures.