27 June 2025

Mosman Oil and Gas Limited

("Mosman" or the "Company")

Drilling Complete at Garcia Prospect

Mosman Oil and Gas Limited (AIM:MSMN) the helium, hydrogen and hydrocarbon exploration, development and production company, announces the completion of the drilling programme at the Garcia prospect.

Garcia Prospect

This well, located in the Garcia prospect, in which Mosman has a 20% working interest, was spudded on 24 June 2025 and reached a total depth of 1,288 feet. Gas testing was conducted continuously using an onsite mass spectrometer. The well encountered water in the principal target, the Lyons formation, at a depth of 1,288 feet. A flow test conducted at the top of the Lyons formation indicated a small percentage of helium, but the flow rate was weak, likely due to tight rock with low porosity. After drilling an additional 3 feet, further water was encountered, leading to the decision to halt further drilling.

In accordance with the agreement negotiated with the landowner, Mosman will convert the well into a water well. The rig crew will demobilise following completion of the water well conversion which is expected to cost no more than $30,000, including the pipe, gravel and rig time. The Company has yet to receive details of the final well cost, but this is not expected to differ materially from pre-drill expectations.

In light of this latest disappointing well result the Company is in discussions with its partners in relation to the continuation of the current Vecta campaign and a further announcement will be made in due course.

Location Map illustrating the five prospects identified by surface mapping within the Project Area.

(Source: Vecta Oil and Gas Ltd.)

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Howard Mclaughlin, Interim Chief Executive Officer of Mosman, said "Given the disappointing results obtained from the Vecta Project thus far we have entered into discussions about potentially concluding the drilling programme early, reflecting our commitment to preserving cash resources and with the intention of allowing us to focus our full attention and financial resources on the Sagebrush and Coyote Wash helium projects. The Company will provide a further update to shareholders next week."

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 the publication of this announcement via Regulatory Information Service ('RIS'), this information is now considered to be 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.