There are companies other than BP that do offshore drilling.
They do however one of the biggest market shares.
BP Plc : Overview
BP ranks in the top three in terms of reserves in the global oil and gas industry with operations in Europe, the Americas, Asia, Australasia and Africa [17]. More than 70% of profits are generated in Europe and the United States but the company is also pressing ahead with new exploration and production operations in Africa, South America, Asia and the Caspian sea [18].
BP is the largest retailer of gasoline in the US. [19] Marketing as AMOCO in the eastern United States and ARCO in the west, it has about 17,150 service stations nationwide [20].
And...SO what?