Size of oil spills
Though the Exxon Valdez spill was the most famous oil tanker spill in U.S. history, worldwide it's only the 35th largest tanker accident, by volume of oil spilled. Improved safety practices and regulations mean that the number and size of tanker spills has been declining for the last three decades. However, larger than any tanker spill are large blowouts like the 1980 Ixtoc I blowout in Mexico and the 2010 Deepwater Horizon spill in the U.S.
The largest loss of oil in history took place during the Persian Gulf War. Retreating Iraqi forces spilled oil directly into the Persian Gulf from an oil terminal and destroyed close to 800 oil wells in Kuwait, causing pressurized oil to erupt, uncontrolled, from the well caps. Fires burned for months at many of the broken wells, consuming even more oil than was spilled.
The data and sources used for this figure can be found in the attached Excel file.