Phase two of resources titan BHP Billiton's Mad Dog jointly-owned project in the Gulf of Mexico looks set to go out in the midday sun after the company's board approved the investment in the oil exploration programme.BHP Billiton's share of the investment, which will facilitate detailed engineering and the procurement of long lead time items related to the hull, topsides and sub-sea equipment, is $708m. UK oil colossus BP, which has a 60.5% stake in the asset, is the operator of the field, while US oil and gas heavyweight Chevron has a 15.6% stake in Mad Dog.The proposed project includes the development of a second spar facility with all sub-sea production and injection wells. The new facility is estimated to have a design capacity of around 130,000 barrels of oil per day that will be exported via the Mardi Gras Pipelines under existing agreements. A final investment decision is anticipated in 2013 with first production scheduled for 2018. JH