Chesapeake Energy Corp.’s long-time COO Steve Dixon, who was named interim CEO in April and held the post until mid-June, left the company Monday with three other top executives, according to a memo sent to employees by CEO Doug Lawler.

The changes were effective immediately, Lawler said. A source for NGI’s Shale Dailyshared the contents of the memo. Lawler, a former Anadarko Petroleum Corp. executive, was hired in May to replace co-founder Aubrey McClendon (see Shale Daily,May 21).

Dixon had been executive vice president (EVP) of operations and geosciences. He joined Chesapeake in 1991, two years after the company was founded, and became COO in 2006. Also leaving Monday were EVP of production Jeff Fisher, Senior Vice President (SVP) of drilling Steve Miller, and SVP and chief of human and corporate resources Martha Burger.

The executives “are leaving the company to pursue other opportunities,” Lawler wrote. “This restructuring will position Chesapeake to be more competitive and focused, and it will further our strategies of financial discipline and profitable and efficient growth from captured resources.”

Lawler told The Oklahoman late Monday that the heave-ho was a “business decision resulting from Chesapeake’s continuing transformation to where we want to be as a top performing company…We have been looking very hard at the executive level and know we need to make changes that are business driven to streamline the company.”

Dixon, McClendon’s long-time exploration and production lieutenant, was named interim CEO after the co-founder retired April 1 (see Shale Daily, April 2). He served in the top spot as part of an interim Office of the Chairman, which also included Executive Chairman Archie Dunham and CFO Nick Del’Osso. When Lawler came aboard in June, the executives resumed their previous duties.

After hiring Lawler, Dunham had said in May that Chesapeake had not missed “a beat” after McClendon left, and he credited the “effective collaboration” between himself, Dixon and Del’Osso. “Steve, Nick, and the rest of the executive group, under Doug’s leadership, will form a highly talented and experienced management team that will lead Chesapeake into its next phase of success and prosperity,” Dunham said at the time.

Dixon’s name and biography had been scrubbed from Chesapeake’s website by the end of business Monday. He often has been credited with finding the source rocks that propelled Chesapeake into becoming the top driller in the United States and second-largest natural gas producer.

In a conference call with analysts early this month to discuss second quarter results, Lawler provided nearly all of the details about the financial and operational results, tasks usually left to Del’Osso and Dixon (see Shale Daily, Aug. 2). The usually loquacious Dixon, who often went into detail about particular wells or particular regions, answered a few questions for analysts. He had led the annual meeting in June (see Shale Daily, June 17).

In that conference call Lawler hinted that big changes were ahead. “A comprehensive company-wide review of our capital allocation and other processes is under way,” Lawler said at the time, “and I believe these initiatives will result in substantial further improvement in both near-term and long-term capital efficiency and returns.”

McClendon has since taken some space at an office building near his former corporate headquarters in Oklahoma City, where he is advancing a new exploration company (seeShale Daily, April 17). Former Chesapeake SVP Tom Price, who headed corporate development and government relations, as well as SVP Henry Hood, who had run land operations, left Chesapeake on May 3. They plan to work with McClendon, according to Chesapeake officials.