Was Opec successful in stopping the slide in oil prices? It depends on how you analyse the numbers.

A look at the Nymex front-month West Texas Intermediate contract, the oil market’s main benchmark, gives the impression of Opec failure. It plunged from $43.60 a barrel ahead of the meeting to close at a 4½-year low of $33.87 at the end of last week. A drop of $10 sounds very much like a vote of no confidence in the cartel.