Nexen Inc. was a Calgary, Alberta–based oil and gas exploration and production company, known for upstream operations spanning Canada’s oil sands, the UK North Sea, the Gulf of Mexico, and offshore West Africa. Formerly Canadian Occidental Petroleum Ltd., the company rebranded as Nexen in 2000 and developed notable assets such as the Long Lake oil sands project and interests in major UK North Sea fields. In 2013, Nexen was acquired by CNOOC Limited; its North American business now operates as CNOOC Petroleum North America ULC, and the Nexen brand has largely been retired.
For the chemical and downstream sectors, Nexen’s relevance lies in supplying crude oil, natural gas, condensate, and natural gas liquids that serve as feedstocks for refining and petrochemical value chains. Historically, Nexen also owned a chlor-alkali and sodium chlorate business, which was spun out in 2005 as Canexus; since then, Nexen’s focus has been predominantly upstream.