A spill containment system for container tanks which include a liquid container and a steel frame surrounding the liquid container. The overall dimensions of the container tank are approximately twenty feet long, eight feet wide and eight and a half feet high. Beneath one or more stacked container tanks is a containment pan assembly including a liquid-tight pan having an interior capable of holding at least a portion of the contents of one liquid container. The containment pan assembly has an upper rectangular section that supports the container tanks and also has a length of about twenty feet and a width of eight feet. However, the entire height of the containment pan assembly is between eight inches and twenty-four inches. Additional similarly constructed containment pan assemblies are arranged adjacent the first assembly with hoses interconnecting the interiors of the several liquid-tight pans of the several containment pan assemblies.