Partners ConocoPhillips and Total have started production at the Surmont 2 in-situ oil sands facility in Canada.
Construction for the facility, which is located at a 63km distance to the southeast of Fort McMurray in the Athabasca region of Alberta, started in 2010.
ConocoPhillips and Total own 50% stake each in the project and it is claimed to be the largest single-phase steam-assisted gravity drainage (SAGD) project ever undertaken by the operator ConocoPhillips.
ConocoPhillips had announced first steam at the facility earlier in the year, which had heated the reservoir to enable conversion of the well pairs to a SAGD configuration, thus allowing the oil flow.
First oil from the facility has been announced following inspection of the product and its successful transfer to sales tanks.
ConocoPhilips chairman and chief executive officer Ryan Lance said: "The oil sands are an important part of our portfolio.
"We're pleased to see a project of this magnitude move from the capital phase to the production phase, knowing that it will produce for decades to come. Achieving this milestone on schedule demonstrates our continued commitment to meet our operational targets."
Production at the facility is expected to rise during 2016 and 2017, increasing production by 118,000 barrels of oil per day (BOD) gross capacity.
Combined oil production for Surmont 1 and 2 sites is expected to go up to 150,000 BOD.
Total Exploration and Production president Arnaud Breuillac said: "This is Total's fifth startup since the beginning of the year, and it contributes to our upstream growth.
"Surmont will produce substantial reserves, with a long plateau that will generate cash flow for decades to come."