The OPEC+ group will decide this weekend on production levels for December, in the first meeting since the United States slapped sanctions on the two biggest oil firms in Russia, a key member of the OPEC+ alliance and its second-largest producer after Saudi Arabia. The producer group led by the Kingdom and Russia has been managing supply to the market for nearly a decade, mostly by restricting oil output to ensure “market stability” in OPEC+ lingo; in other words, to support oil prices or at least put a floor under them. …