Exxon trims its Guyana resource estimate to just under 11 billion barrels

The operator has produced about a billion barrels since 2019 and has not announced a new discovery since early 2024. The number is still enormous, but the direction of travel has changed.

For six years the story of Guyana’s oil has been one of a number that only went up. This week that number moved the other way. ExxonMobil’s estimate of the recoverable resource in the Stabroek block offshore Guyana now stands at just under 11 billion oil-equivalent barrels, Kaieteur News reported on October 2, down from the long-cited figure of more than 11 billion as the company has produced its way through the reservoir.

The explanation is partly arithmetic. Guyana has pumped roughly one billion barrels since production began in 2019, across four floating production vessels operating in the Stabroek block, and barrels produced are barrels no longer sitting in the resource estimate. But there is a second reason the figure has stopped climbing, which is that the discoveries have slowed. ExxonMobil, whose Guyana operation is led by country president Alistair Routledge, has not announced a new discovery in the block since March 2024, after a run that produced 46 finds since 2015.

Exploration has not stopped. The company spent about US$128 million on exploration in 2025, up from US$109 million in 2024, according to the Kaieteur reporting. But rising spending without new discoveries tells its own story about a block that may be approaching the mature phase of its exploration life, where the easy, giant finds have been made and what remains is harder to reach and smaller in scale. That is the normal arc of any oil province. It is simply arriving in Guyana faster than the breathless early coverage implied it would.

None of this threatens the windfall that is remaking Guyana’s economy. Just under 11 billion barrels is still one of the most significant oil resources discovered anywhere this century, and the country’s production and revenue are still climbing as new vessels come online. With crude back above US$100 a barrel, the value of each remaining barrel has rarely looked better. The revision is a recalibration of expectations, not a reversal of fortune.

The pace matters for a country that has organized its entire fiscal future around the Stabroek block. Guyana’s budgets, its borrowing and its ambitions for infrastructure and social spending all rest on assumptions about how much oil will be produced and for how long. A resource estimate that has plateaued is a signal to keep those assumptions conservative, to avoid committing to permanent spending on the strength of a boom that has a visible horizon. The government has repeatedly said it understands this. The discipline of actually doing it is the test every oil state eventually faces, and most of them fail it.

The more sober voices in Guyana have long argued that the resource would not grow forever and that the country should plan for a finite boom rather than an infinite one. Dr. Vincent Adams, a former head of the Environmental Protection Agency and a persistent critic of how the sector has been managed, is among those who have pressed that case. A resource estimate that has stopped rising is a quiet vindication of the argument that Guyana’s task is not to find more oil but to convert the oil it has into lasting wealth, in schools, infrastructure and a sovereign savings cushion, before the barrels run lower. The number came down a little this week. The clock, as it always was, is still running.