—  The opening statement on the website of the Organization of Petroleum Exporting Countries (OPEC) says its members seek ¦ to secure an efficient, economic and regular supply of petroleum to consumers, a steady income to producers and a fair return on capital for those investing in the petroleum industry. To achieve these goals, OPEC attempts to coordinate and unify petroleum policies by raising or lowering its members collective oil production. However, increased production by the United States, Russia, Oman, Mexico, Norway, and other non-OPEC countries has placed downward pressure on the price of crude oil. 
Please explain:
—‹  To achieve these goals of stable and fair oil prices, what must OPEC do to maintain the price of oil at its desired level? 
How easy it is for OPEC to achieve this goal?