Drilling in the previously untested northern segment of the Mad Dog field in the Gulf of Mexico has resulted in a "significant resource extension", according to the oil giant BP.BP now estimates (pending confirmation through future drilling) that the total hydrocarbons now in place in the Mad Dog field total 4m barrels of oil equivalent.The Mad Dog complex also includes an existing field, which has been in production since 2005, and the South field, where appraising drilling was conducted 2008 and 2009."With these additional hydrocarbon resources north of the main field, Mad Dog has been firmly established as a giant field in BP's Gulf of Mexico portfolio, rivalling Thunder Horse in size of resource," said Bob Dudley, BP chief executive. "Working with the industry and regulators, we will apply our enhanced standards of safety, reliability and compliance to all of our Gulf activities as we continue to provide important jobs and energy to the nation."