17 October 2025

Mosman Oil and Gas Limited

("Mosman" or the "Company")

£1.67 Million Placing to Advance US Helium Assets Towards Drill-Ready Status

Mosman Oil and Gas Limited (AIM: MSMN), the helium, hydrogen and hydrocarbon company, confirms it has today raised £1,667,500 (before expenses) by way of a placing of 7,411,111,110 new ordinary shares (the "Placing Shares") at a price of 0.0225p per share (the "Placing Price") (the "Placing").

The Placing was conducted by SP Angel Corporate Finance LLP and CMC Markets UK Plc, acting as Joint Brokers to the Company.

In addition to the Placing, as the Company greatly values the support of its retail shareholders, Mosman also intends to offer its existing eligible retail shareholders the opportunity to participate in a retail offer of new ordinary shares at the Placing Price for up to £500,000 (the "Retail Offer").

The Company will release a separate announcement regarding the Retail Offer and its terms shortly. For the avoidance of doubt, the Placing is separate from and does not form part of the Retail Offer.

Progressing Helium Projects

Mosman continues to advance its portfolio of helium projects in the United States, with Sagebrush and Coyote Wash in Colorado representing the Company's key near-term development priorities.

Funds raised from the Placing, together with the current cash balance of approximately £1.2 million, will be used to continue progressing exploration activity towards establishing the Sagebrush and Coyote Wash projects as drill-ready. The net proceeds of the Placing will be used for:

·      Progressing the Independent Prospective Resource Validation at Coyote Wash (Q4 2025)

·      Activities at Sagebrush, including 3D seismic acquisition and interpretation in Q4 2025, extended well testing through Q4 2025 to Q1 2026, well planning and long lead items, and surface facility design

·      Field operations and administration

·      General corporate purposes

Carl Dumbrell, Chairman of Mosman Oil and Gas, commented: "This successful Placing provides the capital needed to drive the next phase of development across our world-class helium assets in Colorado. The coming quarters will be an exceptionally active period for Mosman as we complete 3D seismic at Sagebrush, progress the Coyote Wash resource validation and prepare for and conduct  extended well testing. We thank our investors for their continued support and look forward to delivering material progress and value creation through Q4 and into 2026."

Admission to AIM and Total Voting Rights

The Placing is conditional, inter alia, upon the Placing Shares being admitted to trading on AIM. Application has been made to the London Stock Exchange for the Placing Shares, which will rank pari passu with the Company's existing issued ordinary shares, to be admitted to trading on AIM and dealings are expected to commence at 8:00 a.m. on or about 23 October 2025.

Following the issue of the Placing Shares, the Company's total voting rights will comprise 30,392,632,772 Ordinary Shares of no par value, and the Company does not hold any shares in treasury. The above figure may therefore be used by shareholders as the denominator for the calculations by which they will determine whether they are required to notify their interest in, or a change to their interest in, the share capital of the Company under the Companies' Articles.

Correction to AGM Voting Date

Further to the Company's recent Notice of Annual General Meeting ("AGM"), Mosman wishes to correct the voting deadline and time for receipt of Forms of Instruction in respect of the AGM, which will be held in Sydney on 10 October 2025.

The second paragraph of the AGM Notice should now read as follows:

"Completed Forms of Instruction must be lodged with the Depositary at The Pavilions, Bridgewater Road, Bristol BS99 6ZY, no later than 2:00 p.m. (London time) on 5 November 2025, being 1:00 a.m. AEDT (Sydney time) on 6 November 2025, or submitted electronically through the CREST voting system in accordance with the instructions set out on the Form of Instruction.

All other shareholders who hold shares directly in the Company's register and not through CREST should either attend the Meeting in person or ensure that their completed Proxy Forms are received by the Company no later than 2:00 p.m. (London time) on 5 November 2025, being 1:00 a.m. AEDT (Sydney time) on 6 November 2025."

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 publication via Regulatory Information Service ('RIS'), this information is now in the public domain

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.

Proposed Change of Name and Ticker
At the forthcoming Annual General Meeting on 10 November 2025, shareholders will be asked to approve the proposed change of the Company's name to Quantum Helium Limited, with a proposed new AIM ticker QHE. The change, once approved and registered with the Australian Securities and Investments Commission (ASIC), will reflect Mosman's strategic focus on helium exploration and development. A further announcement will be made regarding the timetable for the proposed change in due course.