Sinopec unveiled new restrictions on refined oil purchasing to its branches at the end of May which set new test criteria to avoid substandard blends, National Business Daily reports.

As per the new policy, Sinopec's will only include central state-owned refineries, subsidiaries as well as several private refineries in its list of suppliers. Almost one hundred local refiners will be dropped by the change.

Currently, local producers account for 18 percent of China's energy market, analysts said. Previously, China's two energy giants, Sinopec and Petrochina, purchased one to 25 percent of their total refined oil.

"Sinopec has halted its purchase of refined oil products in certain areas, and has improved standards of refined oil supply," a Sinopec executive of told National Business Daily on Wednesday.

Sinopec's new test standards for blended oil now surpass international quality criteria, since they measure indicators for olefin contents and Dimethoxymethane.

據每日財經新聞報道，中石化5月下旬出臺了加強成品油外采的措施，新增了外采油品檢驗標準，嚴防不達標調和汽油進入中石化銷售系統。

目前除幾大央企的煉廠以及控股的煉廠以外，民營企業僅保留了十幾個地煉廠商做為外采油品的生產商，近百家供應商被淘汰。

業內人士認為，目前，兩大巨頭公司在各地外采資源占總資源供應的1%~25%不等，地煉資源供應約占市場的18%。

中石化銷售公司一位高管在接受《每日經濟新聞》專訪時透露，中石化已在部分地區暫停了油品的外采，進一步提高外采油品的質量標準。

此外，新質量標準中增加了針對調和油檢測的若干新的指標。如"烯烴含量""甲縮醛"等一系列檢測指標。