The growing clout of state-backed Chinese oil traders is raising concerns over their influence on the price of crude as trade increasingly flows into markets with little regulatory oversight. Last August, Chinaoil, the trading arm of China National Petroleum Corp., swept up around 90% of the crude then available in the Dubai market, which sets the price of the Middle East’s most important benchmark. That pushed up the price of oil by hundreds of millions of dollars for dozens of Asian refiners, according to industry executives. Chinaoil has bought up more than half the crude being sold in the Dubai market in 10 of the 25 months since January 2014, according to an analysis of data from Platts, the energy information provider that runs the benchmark. A unit of China Petroleum & Chemical Corp. SNP -3.04 % , or Sinopec, sold more than half the oil put on the […]