WASHINGTON — A new federal study has found that an oil leak in the Gulf of Mexico that began 14 years ago has been releasing as much as 4,500 gallons a day, not three or four gallons a day as the rig owner has claimed.

The leak, about 12 miles off the Louisiana coast, began in 2004 when a Taylor Energy Company oil platform sank during Hurricane Ivan and a bundle of undersea pipes ruptured. Oil and gas have been seeping from the site ever since.

Taylor Energy, which sold its assets in 2008, is fighting a federal order to stop the leak. The company asserts that the leaking has been slight — between 2.4 and four gallons per day. Oil plumes from the seafloor, Taylor executives have said, are from oil-soaked sediment that has formed around the platform, and any gas rising from the bottom is the natural product of living organisms.

“The results of this study contradict these conclusions,” the report, issued on Monday by the National Oceanic and Atmospheric Administration and Florida State University, concluded.