Approval Secured for Sagebrush 3D Seismic Survey.

11 August 2025

Mosman Oil and Gas Limited

("Mosman" or the "Company")

Approval Secured for Sagebrush 3D Seismic Survey

Mosman Oil and Gas Limited (AIM: MSMN), advancing helium, hydrogen and hydrocarbon projects in the USA, is pleased to announce that the Ute Mountain Ute Tribe has formally approved the 3D seismic acquisition programme at the Company's flagship Sagebrush Project in Colorado, USA, where Mosman holds an 82.5% working interest.

This approval marks a major milestone in the advancement of Sagebrush, enabling Mosman to move ahead with preparations for the seismic acquisition scheduled to commence in late September and run through mid-October 2025. The 3D seismic survey is a key component in refining drill targets and advancing towards an extended production test at the previously drilled Sagebrush-1 well, which recorded historic helium concentrations of 2.76% from the Leadville Formation.

Meanwhile, Sproule, a globally recognised independent energy consulting firm, is well advanced in its independent verification of the helium resources at Sagebrush. The work includes a comprehensive review of geological and engineering data, with results expected towards the end of August 2025. These findings will further support the Company's commercialisation strategy for the project.

Mosman also anticipates news on the approval for the Coyote Wash Project in the coming weeks. The final Environmental Assessment for Coyote Wash was completed on 17 July 2025 and is currently in the final stages of the permitting process.

Mosman Interim-CEO Howard McLaughlin commented: "We are delighted to have received the Ute Mountain Ute Tribe's approval for the Sagebrush 3D seismic survey, which is a vital step forward in unlocking the project's substantial helium potential. With seismic now set to proceed and the Coyote Wash approval also expected soon, Mosman is entering an exciting period of operational momentum across both key projects."

Market Abuse Regulation (MAR) Disclosure

The information contained within this announcement is deemed by the Company to constitute inside information as stipulated under the Market Abuse Regulations (EU) No. 596/2014 ('MAR') which has been incorporated into UK law by the European Union (Withdrawal) Act 2018. Upon the publication of this announcement via Regulatory Information Service ('RIS'), this information is now considered to be in the public domain.

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Updates on the Company's activities are regularly posted on its website: www.mosmanoilandgas.com

Notes to editors

Mosman (AIM: MSMN) is a helium, hydrogen and hydrocarbon exploration, development, and production company with projects in the US and Australia. Mosman's strategic objectives remain consistent: to identify opportunities which will provide operating cash flow and have development upside, in conjunction with progressing exploration. The Company has several projects in the US, in addition to royalty interests in Australia.