The PEMEX IXTOC 1 spill was probably larger than Deepwater Horizon but political considerations preclude this from ever being recognized. PEMEX estimates of 10,000-30,000 BOPD were kept low by PEMEX and the Mexican government for liability reasons, and the US was sensitive to their predicament.
The press and our leader were interested in demonizing the oil industry during the BP spill so the estimates grew larger and larger as time went on. The later estimates of 100 MMBOPD and 100 MMCFGPD were hardly plausible. If we could make wells capable of sustaining months of production at those rates in the Gulf of Mexico we would be an oil exporter, not an importer.
The main difference between the two was that IXTOC 1 took 9 1/2 months to cap.
At the time the IXTOC spill, located in the Yucatan, affected fishing off the Mississippi delta, and there was great discussion of class action lawsuits against the Mexican government. The US government did not encourage such lawsuits at that time.
Within a year or so the naturally occurring organisms that ‘eat’ oil associated with natural seeps worldwide had dealt with the massive IXTOC spill, and the Gulf of Mexico returned to normal. The press and the US government had access to this information at the time of the BP spill but chose to create catastrophe models unfounded by previous experience. Your tax dollars at work.
http://www.incidentnews.gov/incident/6250