Don L. Blankenship, the embattled chief executive of Massey Energy, resigned Friday in a move that might enable the company to improve relations with federal regulators but might also hasten a takeover. Blankenship, 60, and Massey, one of the country's largest coal producers, have been under fire since an explosion in April at a mine in West Virginia in which 29 workers were killed. The explosion, at the Upper Big Branch mine, was the nation's worst coal mining accident in 40 years. Since then, the company has been hit by civil and criminal investigations and damage suits, and regulators have stepped up investigations of several more company mines for possible safety infractions. 'After almost three decades at Massey, it is time for me to move on,' Blankenship said in a statement. His resignation will be effective Dec. 31. He will be succeeded by Baxter F. Phillips Jr., president of Massey, as chief executive and by retired Adm. Bobby Inman, a former senior Central Intelligence Agency official and the lead independent director on the Massey board, as nonexecutive chairman. Reports of possible takeover bids have been swirling for more than a month. The leading contender for such a takeover has been Alpha Natural Resources, which has made a bid. ArcelorMittal, the world's largest steel company, and Arch Coal have also expressed interest. Several Indian coal companies are thought to be interested in buying assets from Massey. Such a deal would enable Massey to meet rising liabilities that have resulted from the accident and still remain independent. It was not immediately clear what effect Blankenship's surprise resignation would have on the future of the company. Investment bankers with an interest in coal companies have said that Blankenship personally has opposed a takeover. However, his resignation may help soothe the harsh relations between Massey and regulators, which have been stoked by his public and frequent claims that the company's safety measures were more than adequate. He argued that the Upper Big Branch accident was probably caused by leakage of natural gas from a crack in the mine rather than from unsafe mining practices like excess coal dust and impaired monitoring devices. Massey directors have said they are open to a buyout. A company news release gave no hint that Blankenship, who was chairman as well as chief executive, was forced to resign. Phillips thanked Blankenship for his service and said in the statement, 'This is a strong and successful coal company, and I will work hard to match and surpass its success in the future.' Phillips has been president since November 2008. 