BP <BP> STARTS BID FOR STANDARD OIL <SRD> SHARES British Petroleum Co PLC said it has started its previously announced 7.4 billion dlr offer to purchase the 45 pct interest in Standard Oil Co that it does not already own for 70 dlrs per share. In a newspaper advertisement, the company said the offer, which is not conditioned on receipt of any minimum number of shares, and associated withdrawal rights will expire April 28 unless extended. BP said it is asking Standard Oil for the use of its shareholder list in disseminating the offer, on which the Standard board has not yet taken a position.