The group of more than 20 producers agreed to cut an extra 500,000 barrels per day (bpd) to take their target to 1.7 million bpd, or 1.7% of global demand.
Saudi Energy Minister Prince Abdulaziz bin Salman said effective cuts could be as much as 2.1 million bpd as Saudi would carry on cutting more than its quota.
Here is what analysts expect in terms of market response:
Amrita Sen, co-founder, Energy Aspects
* "A tight crude oil market, weak refining margins environment, no excess inventory as such which Saudi Arabia was acutely aware of and yet it also knew the pervasive bearish sentiment that is prevalent, which meant without a “surprise”, the risk to prices correcting lower was significant.
* "They had to protect the downside to prices without over-tightening an already tight physical market. Newly appointed Saudi Energy Minister Abdulaziz bin Salman’s goal was not necessarily to push oil prices significantly higher, but rather to put a firm floor under them during Q1 2020 (fresh on the heels of the Aramco IPO) to temper any seasonal weakness.
* "Saudi Arabia also believes and so do we that OPEC will have to raise production in H2 2020 and hence the shorter tenure."
Phil Flynn, analyst, Price Futures Group
* Unexpected extra cut to provide "strong support" to oil market.
* "The cuts are coming at a time of year when demand will be the strongest and may also add pressure to product prices, especially ultra-low sulfur diesel, ahead of the new IMO 2020 ship fuels.
* "While the market's response may be muted, make no mistake about it, this will give oil a floor."
Ole Hansen, head of commodity strategy, Saxo Bank
* "By agreeing a 500,000 bpd cut based on 2018 levels OPEC has boxed themselves into a corner. In order to achieve compliance the pressure is now on those having produced above their previous limit."
* A 500,000 bpd reduction does not alter the outlook for H1 2020 which, according to IEA data, will remain oversupplied.
* See limited upside potential for prices, Brent likely to be stuck in lower $60s/bbl for foreseeable future.
Frank Schallenberger, analyst, LBBW
* "If the new output cut of 500,000 bpd is just symbolic insofar as the targets are just brought closer to the current output level - then the market will be disappointed and Brent will fall back below $60 per barrel."
* But if the new cut means that another 500,000 bpd are taken from the market - then Brent will stabilise around $65."
* Demand to grow by 900,000 bpd in 2020, but supply to be stronger, leading to a surplus of 800,000 bpd.
* Cut of another 500,000 bpd could shrink surplus to 300,000 bpd.
Hans Van Cleef, senior energy economist, ABN AMRO
* "If indeed OPEC+ confirms the rumoured 500,000 bpd extra production cut ...I think that the markets may be somewhat disappointed. After all, this is only slightly more than the current production level of OPEC+ and could therefore be seen as a formalisation of the over-compliance we have seen in recent months."
* "The most crucial thing for OPEC now seems to be to show unity within the organisation. The cancellation of yesterday's press conference to wait for Russian approval is not very helpful in that respect."
Stephen Innes, chief Asia market strategist, AxiTrader
* "All the knowns were baked into the prices and no shock value. Oil production cut said to be split roughly 2/3 OPEC, 1/3 non-OPEC producers (same ratio as under prior agreement)."
* Adherence to cuts is unlikely.
* "Saudi Arabia strong-armed this one, making it abundantly clear to other OPEC+ participants that it is no longer willing to shoulder the burden of supporting oil prices when others want."
* "I think they won some sympathy from fellow members due to the Aramco IPO ...This is a band-aid on a broken leg and will do little more than subsidise shale oil."
* "At the end of the day, the OPEC straddle (price bottom) remains in place, so there is no fear of prices tanking anytime soon."
Harry Tchilinguirian, global oil strategist, BNP Paribas
* "If we were to have an outcome of an extension of cuts with only the official quota of OPEC+ being reviewed lower, rather than actual production, then the change in supply policy would be cosmetic (given below-target production in some countries, notably Saudi Arabia and Angola)."
* "OPEC would still face imbalances in Q1-Q2 next year suggesting oil inventory builds that can come to negatively impact on oil prices."
* "We suspect that OPEC and its allies understand the dynamic of the choice above and will be considering supply policy in the context of the whole of 2020, not just the first half."
Commerzbank analysts Daniel Briesemann and Carsten Fritsch (Dec. 6)
* See "considerable downside risks" for oil prices.
* "The idea of extending the current agreement until mid-2020 seems to be off the table. In addition, Russia will be allowed to exclude the oil condensates that occur as a by-product of natural gas production when calculating its oil production relevant to the cuts. This corresponds to standard OPEC practice."
* "Thanks to voluntary and involuntary production cuts, OPEC has been producing considerably less than stipulated in the agreement for months. In other words, the latest decisions change very little."
* "We believe that yesterday's decisions (at OPEC meeting) do not go far enough. After all, the oversupply in the first quarter of 2020 is far higher than 500,000 barrels per day. What is more, it remains unclear how the sizeable oversupply that will likewise be seen in the second quarter can be contained without production cuts."
Norbert Rücker, head of economics & next generation research, Julius Baer
* Stick to 'Neutral view', oil prices to trade around $60 per barrel in near term, lower in 2020.
* See soft demand, rising supply from the U.S., Canada, Brazil and the North Sea.
* "Petro-nation oil policy has so far struggled to stem against slower moving market balances and soft demand, especially as oil prices heading towards $70 per barrel would simply re-accelerate the U.S. shale boom."
(Reporting by Swati Verma and Arpan Varghese in Bengaluru; editing by Jason Neely)