International Business Machines Corp., the world's biggest computer maker, said the U.S. Securities and Exchange Commission is examining how the company recorded some sales, possibly because of a probe into a customer.

The formal investigation seeks information on how IBM booked sales in 2000 and 2001, IBM said Monday in a statement. The probe probably is related to a separate SEC investigation of a client of IBM's Retail Store Solutions unit, IBM said.

IBM said its accounting complies with all regulations, and the company is cooperating with the SEC. IBM's accounting is more conservative than most U.S. companies, investors have said. In 1996, the company, based in Armonk, N.Y., began including gains from asset sales and expenses for job cuts in operating expenses instead of breaking the items out as separate charges.

"You trust IBM when they say they've done everything according to the accounting rules," said Ned Riley, chief investment strategist at State Street Global Advisors, which manages about $120 billion and whose parent is IBM's top investor. "You don't put them in the same category as some of the others."

A formal investigation means the SEC can issue subpoenas. The probe covers years when Louis Gerstner Jr. was chief executive officer. Samuel Palmisano became CEO in March 2002.

John Nester, an SEC spokesman, declined to comment. IBM spokesman Joe Stunkard declined to comment beyond the statement. The unit sells computer checkout hardware, software and related services to retailers including Lowe's Cos. and Albertsons Inc.

The company, also the biggest seller of computer-related services and the No. 2 software maker behind Microsoft Corp., has been boosting its disclosure to soothe investors.

Shareholders had criticized IBM for not giving enough detail in financial statements on how it accounts for items such as real-estate and intellectual property sales, said William Batcheller, who helps manage $16 billion for National City Corp., which owns 2.7 million IBM shares.

IBM stock fell 4.6 percent Feb. 15, 2002, after the New York Times said the computer maker didn't fully disclose the effect of a gain from the sale of a product line on earnings.

Three days after the report, IBM said it would expand its accounting information. The company decided to give investors a "road map" to explain data in its 2001 annual report and to shift some items to the "other income" category on its income statement from selling, general and administrative expenses. IBM also started disclosing the effect of pension-related plans.

After the criticisms, IBM has "tried very hard to be very transparent," said John Jacobs, president of Jacobs & Co., which owns IBM shares among the $150 million it manages. IBM now "tends to be overly generous with information with the Street."