 In any case, that made Kerr-McGee's well the first oil discovery drilled out of sight of land.When offshore drilling moved into deeper waters of up to , fixed platform rigs were built, until demands for drilling equipment was needed in the to depth of the Gulf of Mexico, the first jack-up rigs began appearing from specialized offshore drilling contractors such as forerunners of ENSCO International.The first semi-submersible resulted from an unexpected observation in 1961.