Instead, the EPA recommended Chevron “implement all measures” to inject 80 per cent of the carbon dioxide. The absence of a “practicable means” limitation means Chevron cannot use excessive cost as a reason for inaction.

Australia Institute adviser Mark Ogge said Chevron had treated its commitment to store carbon dioxide as optional.

“The EPA is calling them on their promises, and it could finally get more real if the minister acts.”

Chevron must purchase authorised carbon offsets, including Australian carbon credit units, for all reservoir carbon dioxide that is not buried.

The EPA has also recommended that Gorgon’s other emissions of about five million tonnes a year from burning gas to run its plant, be reduced in a straight line from 2025 to zero by 2050, with offsets bought for any exceedance.

Conservation Council of WA executive director Maggie Wood said offsets should only be used as a last resort.

“The science is clear that we need to reduce greenhouse gas emissions as quickly as possible,” Wood said.

The EPA is considering requiring “a deep and substantial reduction” in emissions this decade but the tougher approach has not yet been implemented.

The EPA did not accept Chevron’s argument that tenure and logistical constraints of operating on a nature reserve meant it could not implement some emission reduction measures. The regulator said logistical issues were a commercial matter for Chevron, access to additional land could be requested, and less polluting equipment that would require no more land had been excluded from the original design.

An independent review commissioned by the EPA found that better turbines for generating power and compressing the gas to liquify it could reduce emissions by 1.2 million tonnes a year. Sources close to the matter said some of this technology would be difficult to fit into an existing plant but Chevron is investigating other options that are likely to take some years.

The EPA said it would be a “potentially perverse outcome” if Gorgon’s location on Barrow Island - only approved to allow emissions to be reduced - was now a factor in it not taking action.

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Chevron Australia managing director Mark Hatfield said the US major recognised that expectations for managing greenhouse gases had changed significantly since Gorgon’s current conditions were set two decades ago.

“If endorsed by the minister, the EPA’s recommendations would result in Gorgon having the deepest greenhouse gas emissions reduction trajectory for an LNG project in WA to date,” he said.

The EPA has recommended a net-zero by 2050 trajectory for Woodside’s North West Shelf plant and to issue recommendations for Woodside’s Pluto and Chevron’s Wheatstone plants in the coming months.

Hatfield said Chevron was committed to achieving net-zero emissions at Gorgon, but it was a big challenge with uncertainty about how to achieve long-term reductions.

The EPA did not require Chevron and its partners Shell and ExxonMobil to reduce the emissions from burning of Gorgon’s gas by their customers, known as Scope 3 emissions, as it considered they were not sufficiently within the company’s control.

However, it warned it may recommend that future projects with high direct and indirect emissions not proceed at all, rather than just impose conditions on their operation.

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