Evolving estimates indicate Taylor Energy's 11 year Gulf oil leak worse than company reports

For more than a decade, oil has been leaking into the Gulf of Mexico at the site where a hurricane-triggered mudslide toppled a drilling platform off the coast of Louisiana. An Associated Press investigation has uncovered evidence that the slow-motion spill is far worse than platform owner Taylor Energy Company has publicly reported during its secretive — and costly — government-managed effort to end the leak.

Confronted with an AP analysis that found a recent spike in reported sheen sizes and volumes, the Coast Guard acknowledged it held a workshop last August to improve the methodology employed by a Taylor contractor. The Coast Guard also provided a new leak estimate — based on a new method for estimating sheen sizes — that is at least 20 times greater than one recently touted by Taylor.

The following is a chronology of the leak:

— September 2004: A wave-induced mudslide during Hurricane Ivan topples a Taylor Energy Company-owned drilling platform in the Gulf of Mexico, burying a cluster of 28 wells under mounds of unstable sediment.

— July 2008: The Coast Guard determines that oil leaking at the site of the toppled platform poses a "significant threat" to the environment. The government orders Taylor Energy to perform additional work, including daily monitoring flights over the site.

— October 2008: Based on slick sightings, the Interior Department's Minerals Management Service estimates an average of 22 gallons of oil per day is spilling.

— March 2013: Federal officials estimate the site has been discharging approximately 4,500 gallons per year — or around 12 gallons per day — since flights over the site began in July 2008. This estimate is based on reports submitted to the Coast Guard by a Taylor Energy contractor flying over the site.

— March 2014: The Coast Guard and Interior Department convene a scientific workshop to review leak assessments by Taylor Energy-contracted experts. In a recent court filing, the company says experts assembled for the workshop concluded that the sheens observed at the site contained an average volume of less than 4 gallons per day.

— August 2014: The federal government hosts another workshop with Taylor contractors, this time to review the methodology for estimating slick size and volumes during the monitoring flights. Starting Sept. 1, the contractor's reports employ a new method that provides "a more consistent estimate of sheen estimations," according to a Coast Guard statement.

— April 2015: Confronted with an Associated Press analysis of pollution reports that shows a recent spike in sheen sizes and volume, the Coast Guard releases a new leak estimate based on pollution reports submitted after the August 2014 workshop. The Coast Guard says sheens containing an average of roughly 84 gallons per day have been spotted at the site since September 2014 for a total volume of approximately 16,000 gallons over the past seven months.

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Sources: Government and court records, Coast Guard statements