Shell Oil Company (Shell) (defendant) supplied Brown & Bryant, Inc. (B&B) (defendant), an agricultural chemical distribution business, with pesticides and other hazardous chemicals. Chemical spills and leaks often occurred when the pesticides were transferred from Shell’s tanker trucks to B&B’s bulk storage tanks. As a result, chemicals seeped into the soil and contaminated the groundwater at the site and on an adjacent parcel of land owned by the Burlington Northern & Santa Fe Railway Company (Railroads) (defendant). Shell was aware of the spills and took some remedial measures to ensure safe handling of the chemicals. Nevertheless, the spills continued. The State of California and the federal Environmental Protection Agency (EPA) (plaintiffs) filed suit against defendants in federal court to recoup more than $8 million in cleanup costs under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). The district court and Ninth Circuit Court of Appeals held for the State and EPA and found that Shell liable as an “arranger” for the disposal of hazardous waste with knowledge of the spills and subsequent contamination. Additionally, the district court apportioned cleanup costs on the Railroads at 9 percent rather than imposing joint and several liability. The parties appealed various portions of the lower courts’ decisions. The U.S. Supreme Court granted certiorari to review.