About 6,000 gallons of oil sludge spilled into the Des Plaines River Sunday from a container at Caterpillar Inc.'s [s:cat] hydraulics plant near Joliet, Ill., the company and U.S. Coast Guard officials said. A three-mile section of the river, a major industrial waterway southwest of Chicago, was closed to commercial traffic while the spill was being cleaned up. Caterpillar said the sludge was in wastewater that overflowed from a container. Federal officials estimated 65,000 gallons spilled from the container and 6,000 gallons flowed downhill into the river.