The surprise decision by major oil-producing nations to modestly trim output may spark China to stockpile more oil and could tighten supplies globally this winter,according to industry analysts.In early October,members of the Organization of Petroleum Exporting Countries (OPEC) agreed on a preliminary deal to cut production for the first time in eight years.OPEC will decide at the group's next formal meeting on November 30 in Vienna the details of cutting production by up to 700,000 barrels a day,from a current level of just more than 33 million barrels a day.