Why are we doing offshore drilling?

Oil companies always need to explore for new sources of petroleum. Otherwise, they would run out of oil to sell. The most accessible oil fields in the US were drilled and produced many years ago, in particular Pennsylvania and Texas.

Now, to satisfy the demand for oil, the industry is exploring in much less accessible areas, such as deepwater areas of the Gulf of Mexico, Brazil, Nigeria, Angola, and China. Also, the artic area of Alaska is considered to have considerable hydrocarbon resources.

You can find many references on the internet by searching under peak oil, offshore drilling, and semi-submersibles rigs.