Opec’s long-awaited deal to limit oil output alongside a reduction by Russia will need to be closely monitored, skeptical analysts warned on Wednesday.

The Organization of Petroleum Exporting Countries on Wednesday reached a deal to reduce its output for the first time in eight years.

The reduction by OPEC will be “1.2 million barrels per day, to bring its ceiling to 32.5 million barrels per day,” Qatar’s Energy Minister Mohammed bin Saleh Al-Sada told a news conference in Vienna.

He said that non-member Russia has committed to reducing its output by 300,000 barrels per day, half of a hoped-for 600,000 barrels per day from outside the cartel.

In reaction, oil prices were up around eight percent percent and at levels they had traded for most of the day in expectation of a deal being reached.

Benchmark Brent North Sea crude went back above $50 a barrel — and at more than $49, West Texas Intermediate reached a one-month high.

“What investors are going to look at now is how long the deal will hold, and whether any of the participants will cheat” on the agreed quotas, said Naeem Aslam, analyst at Think Markets.

OPEC members have in the past failed to stick rigidly to agreed quotas in order to preserve market share and in turn revenue levels.

Ahead of the deal, Saudi Arabia’s energy minister Khaled Al-Falih assured that “there will be a mechanism to monitor and ensure full compliance.”

He added that the cartel would set out to “ensure that non-OPEC will also join in with a substantial amount of cut that will add to what OPEC is offering.”

Prestige Economics President Jason Schenker said he did “not expect a cut by the full amount, despite a monitoring committee being put in place.”

But as it stands, “this is the most bullish of deals, and a rise toward $60 is not unlikely in the immediate term,” he said of the likely direction for oil prices with Russia also on board.

Over a period of months ahead of the meeting, OPEC members turned their sights on non-cartel producers, particularly Russia, for a pledge they would also tighten the taps.

Securing a commitment from non-OPEC nations is important because the cartel only produces about a third of the world’s oil, meaning its ability to influence prices is limited.

“Russia has agreed with OPEC three times before to cut production while they have actually increased production instead,” said SEB analyst Bjarne Schieldrop.

Regarding OPEC, analysts were expected to assess independent output data alongside official production figures published by the 14-nation group. Natixis analyst Deshpande Abhishek said secondary reports, such as the amount of oil being placed on tankers leaving OPEC member countries, would be watched.

FXTM analyst Lukman Otunuga said a rise in oil projects was also a good indicator of whether producers were sticking to the agreement.

“An interesting observation may be how oil reacts above $50, a level which could be attractive for US shale to jump back in the markets in full force,” Otunuga.

Wednesday’s announcement marked a reversal of OPEC kingpin Saudi Arabia’s two-year-old strategy of flooding the market to squeeze out rivals, in particular US shale oil producers.

• ­Agence France Presse