On Tuesday, TransUnion, one of the three leading credit-reporting companies in the US, priced its initial public offering at $22.50 a share, implying a market valuation of about $4 billion.

That deal was to buy the company from Madison Dearborn Partners, a private equity firm based in Chicago, and from the Pritzker family. Affiliates of Advent and Goldman will continue to hold a majority of the voting power in the company after the I.P.O.

According to the company, 29.5 million shares were sold in the offering. TransUnion could sell an additional 4.4 million if an overallotment is fully exercised.

Shares of TransUnion are expected to begin trading on the New York Stock Exchange on Thursday. The company had expected to price its I.P.O. at $21 to $23 a share.

TransUnion said that it would use $626.5 million to reduce its debt, which it will be getting in net proceeds.

The Chicago-based company was founded in 1968 as a parent company for the Union Tank Car Company, a railcar leasing company. It expanded into credit reporting a year later. The company offers a variety of information services for businesses and consumers.

It operates in 33 countries in Africa, Asia, Latin America and North America and its competitors are the credit reporting bureaus Equifax and Experian.