This excerpt taken from the CVX 10-K filed Feb 28, 2007.
Acquisition of Unocal Corporation
On August 10, 2005, the company acquired Unocal Corporation (Unocal), an independent oil and gas exploration and production company. This acquisition was accounted for under the rules of Financial Accounting Standards Board Statement No. 141, Business Combinations. Unocals principal upstream operations were in North America and Asia, including the Caspian region. Other activities included ownership interests in proprietary and common carrier pipelines, natural gas storage facilities and mining operations. Further discussion of the Unocal acquisition is contained in Note 2 beginning on page FS-34 of this Annual Report on Form 10-K.