Complex sentence: Iraq Petroleum, along with its operator of oil exploration, Petroleum Development Oman, was owned by European oil giants including Anglo-Iranian Oil's successor British Petroleum which encouraged the British government to extend their support to the Sultan.
Split into simpler sentences: Iraq Petroleum, along with its operator of oil exploration, Petroleum Development Oman, was owned by European oil giants including Anglo-Iranian Oil's successor British Petroleum. They therefore encouraged the British government to extend their support to the Sultan.