The Nippon Oil Corporation (新日本石油株式会社, Shin Nihon Sekiyu Kabushiki-gaisha^?, TYO: 5001), or NOC or Shin-Nisseki (新日石) is a Japanese petroleum company. Its businesses include the exploration, importation, and refining of crude oil; the manufacture and sale of petroleum products, including fuels and lubricants; and other energy-related activities.

Its products are sold under the brand name ENEOS, which is also the name used for its service stations. It is the largest oil company in Japan, and in recent years it has been expanding its operations in other countries.

The company was established 1888 as the "Nippon Oil" (日本石油, Nihon Sekiyu^?), "Nisseki" (日石) for short. In 1999, the company merged with and absorbed the former "Mitsubishi Oil" (三菱石油, Mitsubishi Sekiyu^?). The merged company was called "Nippon Mitsubishi Oil" (日石三菱, Nisseki Mitsubishi^?) until 2002, when it adopted its present name.

In late 2009, Nippon Oil announced its most recent merger activity. An excerpt from the press release is attached: