Key Saudi oil figure Ibrahim al-Muhanna says the historic late-2016 Opec/non-Opec deal to cut output is working, though more slowly than anticipated. An extension beyond March 2018 will likely be needed.

Ibrahim al-Muhanna has taken a more back seat role since the May 2016 retirement of former Oil Minister Ali Naimi, for whom he was both right hand man and key interlocutor. But the distribution by the Saudi Oil Ministry of a key speech he made this week indicates that it represents the...