Largest Oil Spills Affecting U.S. Waters Since 1969 Thousands of oil spills occur in U.S. waters each year, but most are small in size, spilling less than one barrel of oil. Yet since the iconic 1969 oil well blowout in Santa Barbara, California , there have been at least 44 oil spills, each over 10,000 barrels (420,000 gallons), affecting U.S. waters. Most Minnesotans don’t realize that we boast the largest inland oil spill in U.S. history. On this day, March 3, in 1991, the Line 3 pipeline ruptured near Grand Rapids, Minnesota, spilling over 1.7 million gallons of oil, much of which flowed into the Prairie River, after a negligently delayed response by the company.