Diamond Shamrock moved to thwart Pickens.

On the defensive from a takeover bid led by oilman T. Boone Pickens Jr., Diamond Shamrock made a $340-million cash counteroffer to shareholders and announced plans to spin off its refining unit into a separate public company. In addition, William Bricker, chairman and chief executive since 1976, said he will retire once the spinoff is complete in about 90 days. Bricker, 55, will be replaced by Charles Blackburn, 59. He will immediately assume Bricker’s titles of president and chief executive. Bricker said shareholders will get one share of new refining company stock for every four shares of Diamond Shamrock stock.