The pending merger of Chicago-based Amoco Corp. and London-based British Petroleum Co. PLC will, if approved, create the worlds No. 3 oil company. Apparently what the merger will not produce is a clash of business and national cultures. BP is given solid marks for having previously integrated SOHIO (Standard Oil of Ohio) and Mobil Corp.s European refining and marketing operations. And BP already has a smattering U.S. executives among its senior staff. Whats more, John Browne, BPs CEO, has run BP Americas and holds an M.B.A. from Californias Stanford Business School.