NEW YORK (CNN/Money) - CMS Energy Corp. Friday replaced its chairman and CEO and said it is expanding its investigations of energy trades that inflated its revenue by billions of dollars in 2000 and 2001.

William McCormick Jr. resigned as chairman and CEO of the company, effective immediately, and was replaced by Kenneth Whipple, a retired executive from Ford Motor Co. who has been on CMS's board since 1993. McCormick was reelected to the board of directors of CMS, though.

The company said it has appointed a special committee of independent directors to investigate matters surrounding the so-called "round-trip" trades in which there was no impact on cash flow or profits. The company said it would restate 2000 results to eliminate about $1 billion in revenue and expenses due to the round-trip trades. It had already stated it would restate 2001 results to eliminate $4.2 billion in revenue and expense due to $3.3 billion in the round-trip trades.

CMS is not the only company to admit to such questionable trades. Its trading partners Dynegy Inc. (DYN: up $0.24 to $9.44, Research, Estimates) and Reliant Energy Inc. (REI: up $0.63 to $17.98, Research, Estimates) have admitted to trades that are being probed by investigators. A Federal Energy Regulatory Commission probe of bankrupt energy trader Enron Corp. has also revealed the company engaged in such round-trip trades. Williams Cos. (WMB: up $0.12 to $17.78, Research, Estimates) said it did not engage in round-trip trades, although it said a few of its trades are being examined by FERC.

CMS said it is cooperating with a Securities and Exchange Commission investigation of the trades. It said it also faces numerous shareholders suits since it first confirmed its role in the trades May 10.

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The executive change is the second top-level departure at the Dearborn, Mich.-based firm in two weeks. Tamela Pallas resigned as president and CEO of CMS Marketing, Services and Trading Co., the CMS unit that handled the questionable trades.

Trading in CMS (CMS: up $0.75 to $18.45, Research, Estimates) gained about 4 percent after the announcement, but shares are still off almost 5 percent since the May 10 disclosure.