No injuries or fires were reported. The federal Bureau of Safety and Environmental Enforcement said inspectors flying over the site today saw a light sheen covering an area about a half-mile by 50 feet.
However, it was dissipating quickly.
The bureau says the blowout happened south of Grand Isle, about 88 kilometres offshore, where the water depth was reported as 47 metres.
Earlier this month, a gas well flowed for several days before being sealed off the Louisiana coast.
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Today's blowout occurred near an unmanned offshore gas platform that was not currently producing natural gas, said Eileen Angelico, spokeswoman for the bureau.
The workers were aboard a portable drilling rig known as a jackup rig, operated by Hercules Offshore. Hercules said in a news release that it was operating the rig for Walter Oil & Gas Corp.
Walter Oil & Gas reported to the BSEE that the rig was completing a "sidetrack well", a means of re-entering the original well bore, Angelico said.