13 November 2025

Mosman Oil and Gas Limited

("Mosman" or the "Company")

Change of name to Quantum Helium Limited

Mosman Oil and Gas Limited ("Mosman" or the "Company"), advancing helium, hydrogen and hydrocarbon projects in the USA, is pleased to announce that it has changed its name to Quantum Helium Limited.

The Australian Securities & Investments Commission has issued a Change of Name certificate on 13 November 2025, and the name change has become effective immediately.

The change of name has been notified to the London Stock Exchange and trading in the Company's depository interests in respect of ordinary shares under the new company name, Quantum Helium Limited, and new ticker, QHE, is expected to commence at 8.00 a.m. on 14 November 2025.

The Company's LEI, ISIN and SEDOL remain unchanged.

The Company's new website address is https://www.quantum-helium.com and its new social media handle is @QuantumHelium.

Shareholders will be unaffected by the change of name, and any existing certificates representing depository interests bearing the Company's former name remain valid and should be retained for future use.

Carl Dumbrell, Executive Chairman of Quantum Helium, commented: "The adoption of the Quantum Helium name reflects our evolution into a dedicated helium exploration and development company with verified and fast-advancing projects in Colorado's Four Corners region. Our Sagebrush project has already been independently evaluated by Sproule ERCE, while the evaluation process for Coyote Wash is now underway, with results expected before the end of this month. With 3D seismic acquisition about to commence and an extended flow test planned at Sagebrush this quarter, we are entering a very active and potentially value accretive period for the Company. Quantum Helium benefits from proven helium prospective resources, a drilled and cased discovery well, and clear pathways toward commercial production. I'm very optimistic about the opportunities ahead for the Company and our shareholders."

Enquiries:

Notes to editors

Quantum Helium Limited (AIM:MSMN/QHE) is a helium, hydrogen and hydrocarbon exploration, development, and production company with projects in the US and Australia. Quantum'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.