Rost 2-26 recent gas sample records 11.5% helium

Mendell Helium PLC

23 September 2026

Mendell Helium plc

("Mendell Helium" or the "Company")

Rost 2-26 most recent gas sample records 11.5% helium

Mendell Helium (LON: MDH), the helium exploration and production company, is pleased to announce that further gas analyses at its Rost 2-26 well ("Rost 2") in the Fort Dodge area, Kansas have recorded helium concentrations of up to 11.5% in the most recently analysed sample.

Since the commencement of de-watering of Rost 2, the Company has undertaken several multi-sample gas analyses, which, in the Board's view, have been consistently impressive. Across the most recent analyses the recorded helium concentrations have increased with the most recent sample registering 11.5% helium.

During this early de‑watering, Rost 2 is producing low gas volumes with the emerging gas‑to‑water ratio being characteristic of an undersaturated brine regime. As saturated brine with a free gas phase is present in Rost 1-26, approximately 330 feet away, the Company will continue to produce the well and evaluate next steps. Helium concentration is a measure of gas composition only and is not an indication of the volume of gas or helium that Rost 2 may ultimately produce.

Based on results to date, the Company is evaluating whether appropriate well stimulation (fracking) could increase gas volumes and helium recovery. Rost 2 is perforated with an acid stimulation across approximately twenty feet of reservoir. A frack design programme is being prepared with a possible plan for multiple stages across hundreds of feet of reservoir.

As a reminder, the Company utilised a mass spectrometer while drilling the Rost 2 and helium levels were found to be elevated across hundreds of feet of reservoir in both the Morrow and the Mississippian formations. If the current helium enrichment seen at Rost 2 persists, the Company will take steps to stimulate production with fracks in the Morrow and possibly also in the Mississippian. Fracking is likely to produce considerably more water in which case it may be necessary for Mendell Helium to upsize the Rost 2 pump to accommodate up to approximately 10,000 barrels per day.  The Company is fully funded for any additional work that it may undertake at Rost 2.

The Schneweis Ventures 13A ("Schneweis") well continues to produce under its own pressure with gas being delivered directly into a pipeline owned by the Company's joint venture partner, Ritchie Exploration Inc. ("Ritchie").  Schneweis has now been connected to its salt water disposal well and is generating considerable water volumes also without the use of a pump. Ritchie reports that all on-site operations at the disposal well are proceeding satisfactorily. Gas production rates have reached a high of 700 Mcf/day but remain very variable during this de-watering phase.

Further updates will be made in due course as Rost 2 and Schneweis develop.

This announcement contains inside information for the purposes of the UK Market Abuse Regulation and the Directors of the Company are responsible for the release of this announcement.

ENDS

Engage with the Mendell Helium management team directly by asking questions, watching videosummaries and seeing what other shareholders have to say. Navigate to our Interactive Investorwebsite here: https://mendellhelium.com/link/PKa6Ve

Enquiries:

Investor questions on this announcement We encourage all investors to share questions on this announcement via our investor website	https://mendellhelium.com/s/a6a55a
Mendell Helium plc Nick Tulloch, CEO	Via our website investors@mendellhelium.com
Cairn Financial Advisers LLP (Nominated Adviser) Ludovico Lazzaretti / Liam Murray	Tel:  +44 (0) 20 7213 0880
SI Capital Limited (Broker) Nick Emerson	Tel:  +44 (0) 1483 413500
Fortified Securities Guy Wheatley	Tel: +44 (0) 203 4117773
CREST Corporate Broking Jerry Keen	Tel:  +44 (0) 20 3973 3678
AlbR Capital Limited Gavin Burnell / Colin Rowbury / Jon Belliss	Tel: +44 (0) 207 4690930
Brand Communications (Public & Investor Relations) Alan Green	Tel: +44 (0) 7976 431608

Overview of Mendell Helium

Mendell Helium is a helium producer in Kansas, USA where it operates through its wholly owned subsidiary M3 Helium.

M3 Helium's flagship well, Rost 1-26, is in Fort Dodge, just to the east of Dodge City, Kansas. It has been tested as containing 5.1% helium composition and a drill stem test yielded a maximum flow rate of approximately 2,900 Mcf per day. Water removed from Rost 1-26 is delivered to Brobee, a nearby disposal well that has been permitted at 10,000 barrels of water per day at 1,200 psi.  Production at Rost 1-26 commenced in early November 2025 and the most recently recorded flow rate in December 2025 was 250 Mcf per day equating to approximately $1.4 million of helium per year (at $300/Mcf helium).

M3 Helium has subsequently drilled a second well, Rost 2-26, which is currently being de-watered and early results have been encouraging. It also owns additional leases in the Fort Dodge area capable of supporting up to eight new production wells. It has also agreed a joint venture with Ritchie Exploration, Inc. to recomplete the Schneweis Ventures 13A, a well with a drill stem test of over 10,000 Mcf per day and a historic flow rate of 300 Mcf per day. Since coming back on line, the well has recorded peak flow rates of up to 700 Mcf per day, although rates have been inconsistent during de-watering.

At the Rost wells in Fort Dodge, M3 Helium treats the raw gas on site to concentrate the helium and has leased two tube trailers which it uses for deliveries to its offtaker.

M3 Helium also has interests in five producing wells (Peyton, Smith, Nilson, Bearman and Dimmitt) within the Hugoton gas field in South-Western Kansas, one of the largest natural gas fields in North America. Significantly these wells are in the proximity of a gathering network and the Jayhawk gas processing plant meaning that producing wells are all tied into the infrastructure.

Forward Looking Statements

These forward-looking statements are not historical facts but rather are based on the Company's current expectations, estimates, and projections about its industry; its beliefs; and assumptions. Words such as 'anticipates,' 'expects,' 'intends,' 'plans,' 'believes,' 'seeks,' 'estimates,' and similar expressions are intended to identify forward-looking statements. These statements are not a guarantee of future performance and are subject to known and unknown risks, uncertainties, and other factors, some of which are beyond the Company's control, are difficult to predict, and could cause actual results to differ materially from those expressed or forecasted in the forward-looking statements. The Company cautions security holders and prospective security holders not to place undue reliance on these forward-looking statements, which reflect the view of the Company only as of the date of this announcement. The forward-looking statements made in this announcement relate only to events as of the date on which the statements are made. The Company will not undertake any obligation to release publicly any revisions or updates to these forward-looking statements to reflect events, circumstances, or unanticipated events occurring after the date of this announcement except as required by law or by any appropriate regulatory authority.

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