(Yicai Global) Sept. 17 -- Petroleum-related stocks bucked the trend this morning as stock markets on the Chinese mainland began the morning down.

The Shanghai Composite Index started 0.23 percent lower at 3,023.71. The Shenzhen Composite Index opened 0.28 percent down at 9890.58, and the ChiNext Price Index, which tracks emerging companies listed in Shenzhen, began 0.21 percent lower at 1,710.77. Just six stocks listed on the Star Market, Shanghai's new board for innovative science and tech companies, opened higher.

Oil stocks have been roaring this week after an attack on two Saudi Arabian oil facilities threatened to hamper supplies and push prices up. The precious metals and agriculture sectors were the biggest losers.