Sproule to Verify Coyote Wash Helium Resource

7 November 2025

Mosman Oil and Gas Limited

("Mosman" or the "Company")

Sproule Engaged to Independently Verify Coyote Wash Helium Resource

Mosman Oil and Gas Limited (AIM: MSMN), advancing helium, hydrogen and hydrocarbon projects in the USA, is pleased to announce that it has formally engaged independent consultant Sproule ERCE to undertake a Competent Person's Report (CPR) of the Coyote Wash Project in Colorado, USA, in which it owns 100% working interest.

This engagement follows Mosman's recently announced internal best estimate of 1,072 MMcf (million cubic feet) of 2U gross prospective helium resources across six mapped Leadville helium prospects at Coyote Wash (RNS dated 13 October 2025).

Highlights

· Sproule ERCE formally engaged to independently verify Mosman's internal Coyote Wash helium resource estimate under SPE PRMS standards.

· Work scope includes assessment of helium, CO₂ and hydrocarbon resources across eight mapped structures.

· Final report expected in late November 2025, which would provide Mosman with its second verified helium resource in Colorado.

· Follows Sproule's independent verification of the Sagebrush Project completed in September 2025.

Background

Under the executed project schedule, Sproule ERCE will review Mosman's technical dataset, including 3D seismic interpretation, petrophysical analysis, and well data from the Coyote Wash 30-12 well and offset analogues.

The scope of work includes a full CPR of the prospective helium, CO₂ and hydrocarbon resources across eight mapped structures in the project area, using Sagebrush reservoir parameters as an analogue.

Howard McLaughlin, Chief Executive Officer of Mosman, commented: "We're very pleased to again be working with Sproule, this time to verify our internal helium resource estimate at Coyote Wash. This review will mark Mosman's second independently verified helium resource, following Sproule's certification of Sagebrush earlier this year - a major milestone that reinforces the credibility and depth of our Colorado portfolio. Coyote Wash already represents over one billion cubic feet of best-estimate helium resources across six defined prospects. Independent verification will provide additional confidence in those figures and allow us to advance detailed planning for drilling and development. With two verified helium projects, one drilled and cased well ready for testing, and 3D seismic expected to commence this quarter, Mosman is now in a strong, strategic position - ahead of many peers in terms of resource definition and proximity to potential production. We're building a substantial helium business with clear momentum and tangible value catalysts ahead."

Enquiries:

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.