A private equity consortium of Carlyle Group LP (CG.O) and Warburg Pincus LLC is in advanced talks to acquire privately held credit rating agency DBRS Ltd for more than $500 million, according to people familiar with the matter.

After final bids were submitted this week, Carlyle and Warburg Pincus have so far prevailed in the auction for DBRS, which also attracted Canadian private equity firm Birch Hill Equity Partners Management Inc, the people said on Friday.

No exclusivity has been awarded to any bidder and the outcome could still change, the people cautioned. Carlyle and Warburg Pincus are in the lead partly because they have a global footprint that can help DBRS expand further internationally, one of the people said.

The sources asked not to be identified because the negotiations are confidential.

Carlyle, Warburg Pincus and DBRS declined to comment, while Birch Hill did not respond to a request for comment.

DBRS owner Walter Schroeder, who founded the firm in 1976 and is now in his 70s, hired investment bank Perella Weinberg Partners LP to run an auction for the firm, Reuters first reported in August. It was not immediately clear on Friday what equity stake Schroeder would retain in DBRS, if any.

Toronto-based DBRS is the world's fourth-largest credit rating agency after Standard & Poor's Financial Services LLC, Moody's Corp and Fitch Ratings Inc.

It rates the debt of companies, local authorities and countries, as well as structured finance products such as commercial mortgage-backed securities.

DBRS got a modest start 30 years ago in Toronto, when Schroeder left a Bay Street investment dealer to start rating short-term commercial paper. Two years later, the firm began covering corporate and sovereign debt.

While Standard & Poor's, Moody's and Fitch still account collectively for more than 95 percent of the ratings market, DBRS, with a 2 percent market share, has focused on structured finance products, countries and financial institutions, although it rates all asset classes.

Daniel Curry, a former Moody's managing director, currently serves as chief executive officer of DBRS.

In a Reuters interview in 2007, Schroeder said he had regularly received overtures to acquire the company but was not interested at that stage.

"For the time being, we're fine with the way we are. It would probably take quite an overwhelming offer of some sort to get me to change my mind," Schroeder said at the time.

Private equity firms have shown strong interest in acquiring financial services companies in recent years. A consortium led by Carlyle Group LP acquired financial advisory and investment banking firm Duff & Phelps Corp last year, while CVC Capital Partners bought restructuring advisory firm AlixPartners LLP in 2012.

Private equity firms tend to partner on deals if the equity contribution required is too sizeable for their own funds and investors.

In this case, however, Carlyle's and Warburg Pincus' partnership was driven by the relationship between Olivier Sarkozy, Carlyle's head of the global financial services group, and Michael Martin, his counterpart at Warburg Pincus, one of the people said. Both worked as investment bankers at UBS Group AG (UBSG.VX).