Westwood Pharmaceuticals, Inc. (Westwood) (plaintiff) bought land from National Fuel Gas Distribution Company (National) (defendant). Iroquois Gas Corporation (Iroquois) had sold the land to National under a land-sales contract. After discovering contaminants in the soil, Westwood brought suit against National to recover cleanup costs. National asserted the third-party defense under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), 42 U.S.C. § 9607(b)(3), claiming that Iroquois was responsible for the contamination and cleanup costs. Under CERCLA, a defendant was not liable for contamination caused by the act or omission of a third party other than “one whose act or omission occur[ed] in connection with a contractual relationship” with the defendant. Westwood filed a motion for summary judgment, arguing that because National had a contractual relationship with Iroquois, National could not maintain the third-party defense under CERCLA. The district court denied Westwood’s motion for summary judgment. Westwood appealed.