The phrase "large spill" refers to a significant amount of liquid that has accidentally poured or leaked, creating a mess or potentially harmful situation. Full definition
In the event, although this was the world's eleventh largest spill, less than 1 per cent of the oil reached shore. (newscientist.com)
The only larger spill occurred during the 1991 Gulf War, when Iraq dumped — deliberately — up to 462 million gallons of oil into the Persian Gulf. (discovermagazine.com)