Chinese police said seven of the nine people arrested were from China Petroleum & Chemical Corp., known also as Sinopec, which owns the pipeline. Two others were city managers from Qingdao, where the incident occurred, China's official Xinhua News Agency reported Tuesday.
Details of the charges weren't reported.
Xinhua reported first responders were still conducing search and rescue operations in the region. Friday's accident left at least 55 people dead and 145 injured. The Chinese report said at least nine people are missing.
The Sinopec pipeline spilled crude oil into the city's storm drainage system, which leads to Jiaozhou Bay. No cause was given for the blast. Xinhua reported about 32,000 square feet of water were soiled by the spill.
The 150-mile-long pipeline, called Donghuang II, went into service in 1986. It can carry 73 million barrels of oil per year.
Chinese President Xi Jinping called for "large-scale safety check" following the incident.