Changqing Oilfield Company (PCOC) of China Oil and Gas Co., Ltd. is referred to as China Oil Changqing Oilfield, Changqing Oilfield Company and Changqing Oilfield for short. Established in April 1970 and headquartered in Xi 'an, Shaanxi Province, it is the largest oil and gas field in China. The exploration area is mainly in the Shaanxi-Gansu-Ningxia Basin, with a total exploration area of about 370,000 square kilometers. The exploration, development and construction of oil and gas started at 1970, and 22 oil and gas fields were discovered successively, including 19 oil field, with a cumulative proven oil and gas geological reserve of 541888 million tons (including proven natural gas reserves of 233.008 billion cubic meters, including converted crude oil reserves). In 20 19, Changqing Oilfield produced a total of 2410.6 million tons of crude oil and 410.2 billion cubic meters of natural gas, equivalent to 5.7110,000 tons of oil and gas, making it the largest oil and gas field in China.