Oil ended slightly firmer after volatile trading on Friday, supported by expectations that the Organization of the Petroleum Exporting Countries would agree to cut output next month, though prices fell for the sixth straight week amid global oversupply concerns.  OPEC kingpin Saudi Arabia is keen for the major producers to cut output by about 1.4 million barrels per day, around 1.5 percent of global supply, to support the market, sources told Reuters this week. But other producers, including Russia, have been reluctant to agree to a cut. Brent settled up 14 cents, or 0.2 percent, at $66.76 a barrel. The global benchmark fell 4.6 percent in the week, the sixth consecutive decline. U.S. […]