23 October 2025

The following correction is being made to the total voting rights figure included in the "£500,000 Fully Subscribed Retail Offer to Advance US Helium Projects" announcement released on 22 October 2025 at 7.01 a.m. under RNS Number : 2952E. The RNS should have stated that " Following the issue of the Retail Offer Shares, the Company's total voting rights will comprise 32,614,854,994 ordinary shares of no par value, and the Company does not hold any shares in treasury." All other details remain unchanged. The full amended text is shown below.

£500,000 Fully Subscribed Retail Offer to Advance US Helium Projects

Mosman Oil and Gas Limited (AIM: MSMN), advancing helium, hydrogen and hydrocarbon projects in the USA, is pleased to announce that, further to its announcement of 17 October 2025, the Company has successfully raised £500,000 (before expenses) through a fully subscribed Retail Offer of 2,222,222,222 new ordinary shares of no par value each ("Retail Offer Shares") at an issue price of 0.0225p per share (the "Issue Price").

The Retail Offer, conducted via CMC CapX, provided eligible retail shareholders with the opportunity to participate on the same terms as the institutional placing announced on 17 October 2025.

Together with the £1.67 million placing, Mosman has now raised a total of £2.17 million (before expenses).

Carl Dumbrell, Executive Chairman of Mosman Oil and Gas, commented: "We are delighted with the strong response from our retail shareholders, whose continued support and confidence in Mosman's plans has resulted in a fully subscribed offer. Alongside the recent £1.67 million placing, this brings total funds raised to £2.17 million, leaving Mosman well financed to advance our world-class helium portfolio in Colorado.  We now look to a period of significant news flow including the forthcoming 3D seismic and extended well test programmes at Sagebrush, as well as continued development activity at Coyote Wash. With strong cash backing and two high-quality helium assets, Mosman is in a great position to deliver meaningful development milestones through the coming months."

Admission to AIM and Total Voting Rights

The Retail Offer is conditional, inter alia, upon the Retail Offer Shares being admitted to trading on AIM. Application has been made to the London Stock Exchange for the Retail Offer Shares, which will rank pari passu with the Company's existing issued ordinary shares, to be admitted to trading on AIM, with dealings expected to commence at 8:00 a.m. on 27 October 2025.

Following the issue of the Retail Offer Shares, the Company's total voting rights will comprise 32,614,854,994 ordinary shares of no par value, and the Company does not hold any shares in treasury. The above figure may be used by shareholders as the denominator for calculating notifiable interests in the Company.

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

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

This announcement should be read in its entirety. In particular, the information in the "Important Notices" section of the announcement should be read and understood.

 Important Notices

The contents of this announcement have been prepared by and issued by the Company and is the sole responsibility of the Company. The Board of Directors of the Company are responsible for arranging the release of this announcement on behalf of the Company.

This announcement is not for publication or distribution, directly or indirectly, in or into the United States of America. This announcement is not an offer of securities for sale into the United States.  The securities referred to herein have not been and will not be registered under the U.S. Securities Act of 1933, as amended, and may not be offered or sold in the United States, except pursuant to an applicable exemption from registration. No public offering of securities is being made in the United States.

This announcement and the information contained herein is not for release, publication or distribution, directly or indirectly, in whole or in part, in or into or from Australia, Canada, Japan, the Republic of South Africa, or any other jurisdiction where to do so might constitute a violation of the relevant laws or regulations of such jurisdiction.

The distribution of this announcement may be restricted by law in certain jurisdictions and persons into whose possession any document or other information referred to herein comes should inform themselves about and observe any such restriction. Any failure to comply with these restrictions may constitute a violation of the securities laws of any such jurisdiction.

CMC CapX is a software and technology platform owned and operated by CMC Markets UK plc (trading as CMC CapX) (registered address at 133 Houndsditch, London, EC3A 7BX). CMC Markets UK plc ("CMC") is authorised and regulated in the United Kingdom by the FCA, is acting exclusively for the Company and for no-one else and will not regard any other person (whether or not a recipient of this announcement) as its client in relation to the Retail Offer and will not be responsible to anyone other than the Company for providing the protections afforded to its clients, nor for providing advice in connection with the Retail Offer, Admission and the other arrangements referred to in this announcement.

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.