11.   In fact, companies were discussing the need to curtail refinery output in order to make more money, the documents suggest.

12.   OPEC has complained that whenever it curtails output to boost crude prices, Russia increases its market share.

13.   So far only Russia has agreed to curtail output along with OPEC, and even that has been a meager contribution.

14.   The suddenness with which the U.S. economy began sputtering this winter appears to have galvanized OPEC into curtailing output.