Occidental Petroleum is starting a bidding war for Anadarko Petroleum, making a $38-billion counteroffer in attempt to break up the proposed takeover by Chevron. Occidental said Wednesday it’s offering $76 a share in cash and stock, a premium of about 20% over Chevron’s April 12 agreement to buy The Woodlands, Texas-based Anadarko. That compares with the $33-billion deal, or about $65 a share, agreement that Chevron announced two weeks ago.