Barclays said in a note to clients on Monday that it expected an extension of output curbs from an OPEC-led consortium of countries when they meet on November 30.
The investment bank said it expected a six- or even nine-month extension of production cuts - but added that the level of production cuts would be more significant than the duration.
"Whether or not the countries extend and the duration of the deal are not the relevant questions in our view. We believe the level of the cut is what really matters, and we assign a low likelihood to this detail being announced on November 30," Barclays analysts said in a research note.
The British bank forecast that Brent crude would remain above $60 a barrel during the fourth quarter, but said the benchmark price would fall back to $55 a barrel in 2018. On Monday, Brent crude was 0.25% higher at $63.65 a barrel, while WTI fell 0.78% to $58.49.
The research note continued: "The sustainability of the deal depends on how much longer Saudi Arabia, Russia, Iran and Kuwait are willing to sacrifice market share in the pursuit of revenue and market stability."