29 September 2025

Mosman Oil and Gas Limited

("Mosman" or the "Company")

Appointment of Chief Executive Officer and Board Update

Mosman Oil and Gas Limited (AIM: MSMN), advancing helium, hydrogen and hydrocarbon projects in the USA, is pleased to announce the appointment of Howard McLaughlin as Chief Executive Officer (non-board).

In addition, Carl Dumbrell, currently Chairman, will now serve as Executive Chairman, and Andrew Scott, currently Non-Executive Director, will take on the role of Executive Director.

Appointment of Chief Executive Officer

Howard McLaughlin has been with Mosman since 2017 as Manager of US Operations, overseeing field activity and project development. He was instrumental in Mosman's strategic move into the helium sector in North America, introducing both the Sagebrush and Coyote Wash Helium Projects in Colorado.

Howard has a strong personal alignment with shareholders through his direct investment in Sagebrush, providing clear motivation to see the project successfully developed. He has served as Interim CEO since June 2025 and now formally steps into the CEO role.

Howard brings decades of technical, operational and commercial expertise, having spent 19 years at BHP Petroleum, ultimately serving as Vice President of Global Exploration. He is also a former Managing Director and CEO of an ASX-listed public company, with extensive international experience across Australia, Europe, Africa, the Middle East, Asia and North America.

Carl Dumbrell, Executive Chairman of Mosman, commented: "We are delighted that Howard has agreed to become Mosman's CEO. His personal investment in Sagebrush and his long-standing commitment to Mosman since 2017 make him the ideal person to lead the Company. Over the coming months we will reach important milestones, including the start of 3D seismic over Sagebrush in October and the extended well test on Sagebrush-1 in Q4. Together with progress at Coyote Wash, these steps mark the beginning of an exciting new chapter for Mosman. With an independently verified helium resource and a clear pathway to development, the Company is well positioned for future value creation and we move forward with confidence."

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.