Occidental challenges Chevron with higher bid for Anadarko

Occidental Petroleum launched a campaign on Wednesday to buy Anadarko Petroleum in a hostile takeover, challenging Chevron's proposed acquisition in a battle over key US shale assets.Shares of Anadarko surged, while Chevron and Occidental both fell, suggesting investors believe the proposal could launch a bidding war between global heavyweight Chevron and the much smaller Occidental, which is based in Houston.The latter said it was repeatedly spurned by Anadarko despite offering more money in th