Shengli Oil Fields is China's second largest oil field complex after PetroChina's Daqing Oil Fields and is Sinopec Corp's largest domestic asset. It comprises of oil and gas fields in the Shandong Province northeast China. The main producing reservoirs are the Cenozoic Guantao and Shahejie formations. The Gudong Shengtuo Gudao Kenxi and Chengdao fields contribute to most of the oil production. These fields were developed in the early 1960s and have reached maturity.