Ten oil nations outside OPEC have pledged continued cooperation with the cartel to buoy prices, but difficult decisions lie ahead on how to achieve this.

Officials of the non-OPEC group, which includes such heavyweights as the Soviet Union and Mexico, met in London Tuesday but rejected market suggestions they might not have fully implemented export curbs which they pledged for April-June to reinforce OPEC supply restraint and help boost prices.A signal event will be an OPEC conference in Vienna June 5 in which the cartel must set its output ceiling for the second half of 1989.