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.

据每日财经新闻报道，中石化5月下旬出台了加强成品油外采的措施，新增了外采油品检验标准，严防不达标调和汽油进入中石化销售系统。

目前除几大央企的炼厂以及控股的炼厂以外，民营企业仅保留了十几个地炼厂商做为外采油品的生产商，近百家供应商被淘汰。

业内人士认为，目前，两大巨头公司在各地外采资源占总资源供应的1%~25%不等，地炼资源供应约占市场的18%。

中石化销售公司一位高管在接受《每日经济新闻》专访时透露，中石化已在部分地区暂停了油品的外采，进一步提高外采油品的质量标准。

此外，新质量标准中增加了针对调和油检测的若干新的指标。如"烯烃含量""甲缩醛"等一系列检测指标。