Sea Lion Reserves Evaluation

Rockhopper Exploration plc

26 August 2026

FOR IMMEDIATE RELEASE. THIS ANNOUNCEMENT CONTAINS INSIDE INFORMATION.

26 August 2026

Rockhopper Exploration plc
("Rockhopper" or the "Company")

Sea Lion Independent Recoverable Reserves and Resources Evaluation

Rockhopper (AIM: RKH), the oil and gas company with key interests in the North Falkland Basin, is pleased to announce the results from an updated independent technical report conducted by Netherland, Sewell & Associates, Inc. ("NSAI") on behalf of Rockhopper on the Company's Sea Lion field (the "New Report"). The Report is effective as at 31 July 2026.

The New Report shows that overall gross resource volumes and Net Present Values have increased when compared with the Company's previous independent resource evaluation, also conducted by NSAI, effective December 2025, and announced on 2 April 2026 (the "December 2025 Report").

Importantly, the New Report incorporates the newly accelerated Central Development Area ("CDA") which the Operator intends to develop utilising the OSX-1 FPSO.  The increase in resources combined with the acceleration of development at the CDA and updated commodity price assumptions has led to a significant increase of approximately $788 million in the 2P + 2C Net Present Value of the Rockhopper 35% interest in the Sea Lion development.

A summary of the Key Information (oil only) is provided below:

Reserves

Summary of Gross and Working Interest Net Recoverable Reserves and Future Net Revenue attributable to Sea Lion Field NDA Phases 1 and 2

Rockhopper holds a 35 per cent working interest in the Sea Lion field.

	Oil (MBBL) Gross (100%)	Oil (MBBL) Working Interest (35%)	Future Net Revenue Working Interest (35%) (US$000) Undiscounted	Future Net Revenue Working Interest (35%) (US$000) NPV10
Proved Undeveloped (1P)	231,705.0	81,096.8	2,399,495.1	927,773.3
Probable	82,546.5	28,891.3	999,368.1	248,055.1
Proved + Probable (2P)	314,251.5	109,988.0	3,398,863.3	1,175,828.4
Possible	93,915.5	32,870.4	1,449,350.3	329,433.9
Proved + Probable + Possible (3P)	408,167.0	142,858.5	4,848,213.5	1,505,262.3

Note: Oil volumes are expressed in thousands of barrels (MBBL). Gross (100%) figures represent total field reserves; working interest figures represent Rockhopper's 35 per cent share. Future net revenue is after deductions for Rockhopper's share of state royalties, capital costs, abandonment costs, operating expenses and estimates of Falkland Islands corporate income taxes. NPV10 represents future net revenue discounted at an annual rate of 10 per cent. NPV10 should not be construed as the fair market value of the properties. All figures are based on the Base Price Case. See Economic Parameters below.

Contingent Resources

The contingent resources figures below are unrisked - they have not been adjusted for the probability of commercial development. These estimates should not be aggregated with reserves without extensive consideration of the differing degrees of technical and commercial risk.

Unrisked Gross (100%) Contingent Resources - Oil (MBBL)

	Low Estimate (1C) MBBL	Best Estimate (2C) MBBL	High Estimate (3C) MBBL
Development Pending	264,157.6	461,826.9	608,409.3
Development On Hold	65,168.6	131,318.8	222,543.1
Development Not Viable	11,649.9	32,959.4	95,310.4
Total	340,976.1	626,105.1	926,262.7

Unrisked Working Interest (35%) Contingent Resources - Oil (MBBL)

	Low Estimate (1C) MBBL	Best Estimate (2C) MBBL	High Estimate (3C) MBBL
Development Pending	92,455.2	161,639.4	212,943.3
Development On Hold	22,809.0	45,961.6	77,890.1
Development Not Viable	4,077.5	11,535.8	33,358.6
Total	119,341.6	219,136.8	324,192.0

Summary of Unrisked Working Interest (35%) Contingent Cash Flows after Falkland Islands Taxes

Economic analysis has been performed on the Development Pending contingent resources only.

	Total (US$000) Undiscounted	NPV10 (US$000)
Low Estimate (1C)	2,849,710.0	926,027.1
Best Estimate (2C)	6,043,558.0	1,781,157.9
High Estimate (3C)	8,265,980.9	2,182,437.8

 Economic Parameters

The New Report has been prepared using the following Base Price Case oil price parameters, based on Brent Crude prices adjusted for quality, transportation fees and market differentials:

Period Ending	Oil Price (US$/Barrel)
31 December 2026	82.99
31 December 2027	76.74
Thereafter	75.95

The development pending contingent resources are associated with the proposed development plans for Sea Lion Field and are expected to be produced prior to the economic limit of the field; these plans comprise the CDA Phases 1 and 2 and NDA Phase 3.

For the purposes of this report, the development scenario assumes that once field-level production declines below 125,000 barrels of oil per day, the Aoka Mizu FPSO lease will be terminated and the OSX-1 FPSO will service Sea Lion Field by itself.

Additional Notes

NSAI has also provided estimates of gross and working interest (i) Contingent Gas Resources and (ii) Prospective Oil and Gas Resources. These have not been reproduced in this announcement as there is no plan in place for their development.

The information set out above does not constitute the New Report, but is derived from the New Report. A full copy of the New Report will be available on Rockhopper's website later today: www.rockhopperexploration.co.uk.

Resource Disclosure

The New Report has been prepared in accordance with the definitions and guidelines set forth in the 2018 Petroleum Resources Management System ("PRMS") approved by the Society of Petroleum Engineers ("SPE"). The estimates of reserves and resources included in this announcement have not been adjusted for risk.

Lucy Williams (BSc Geology, MSc Petroleum Geology, Chartered Geologist), the Company's Geoscience Manager, has reviewed and approved the technical information contained within this announcement.

Enquiries:

Rockhopper Exploration plc

Sam Moody - Chief Executive Officer

Tel. +44 (0)20 7390 0230 (via Vigo Consulting)

Canaccord Genuity Limited (NOMAD and Joint Broker)

Henry Fitzgerald-O'Connor / James Asensio / Charlie Hammond

Tel. +44 (0)20 7523 8000

Peel Hunt LLP (Joint Broker)

Richard Crichton / Georgia Langoulant

Tel. +44 (0)20 7418 8900

Vigo Consulting

Patrick d'Ancona / Ben Simons / Fiona Hetherington

Tel. +44 (0)20 7390 0234

Notes to Editors

Rockhopper Exploration plc is a UK-based oil and gas exploration and production company with key interests in the Falkland Islands. The Company holds a 35 per cent interest in licences in the North Falkland Basin, where it has sanctioned the development of the significant Sea Lion field, originally discovered by the Company in 2010.

Rockhopper's shares are quoted on the AIM market of the London Stock Exchange under the ticker RKH.

For more information, visit the Company's website at www.rockhopperexploration.co.uk.

Glossary

Term	Definition
1C	Low estimate scenario of contingent resources; there is at least a 90% probability that the quantities actually recovered will equal or exceed the 1C estimate.
2C	Best (most likely) estimate scenario of contingent resources; there is at least a 50% probability that the quantities actually recovered will equal or exceed the 2C estimate.
3C	High estimate scenario of contingent resources; there is at least a 10% probability that the quantities actually recovered will equal or exceed the 3C estimate.
1P / Proved	Proved Reserves - those quantities of petroleum that, by analysis of geoscience and engineering data, can be estimated with reasonable certainty to be commercially recoverable from known reservoirs under defined conditions.
2P	Proved + Probable Reserves. The sum of 1P and Probable Reserves.
3P	Proved + Probable + Possible Reserves. The sum of 2P and Possible Reserves.
CDA	Central Development Area of the Sea Lion field.
Contingent Resources	Those quantities of petroleum estimated, as of a given date, to be potentially recoverable from known accumulations by application of development project(s) not currently considered to be commercial owing to one or more contingencies.
FID	Final Investment Decision - the decision by the joint venture to commit to full-scale project execution, having secured all necessary approvals and funding.
FPSO	Floating Production Storage and Offloading vessel.
MBBL	Thousands of barrels of oil.
MMBBL	Millions of barrels of oil (= 1,000 MBBL).
NDA	Northern Development Area of the Sea Lion field.
NPV10	Net present value of future net revenues discounted at an annual rate of 10 per cent. NPV10 should not be construed as the fair market value of the properties.
NSAI	Netherland, Sewell & Associates, Inc., independent petroleum engineers.
PRMS	2018 Petroleum Resources Management System approved by the Society of Petroleum Engineers (SPE) - the industry standard framework for the classification and categorisation of petroleum reserves and resources.
Reserves	Those quantities of petroleum anticipated to be commercially recoverable by application of development projects to known accumulations from a given date forward under defined conditions. Reserves must be discovered, recoverable, commercial, and remaining as of the evaluation date.
SPE	Society of Petroleum Engineers.
bbl/d	Barrels of oil per day.

The information contained within this announcement is deemed by the Company to constitute inside information as stipulated under Article 7 of the Market Abuse Regulation (EU) No. 596/2014 (as amended) as it forms part of the domestic law of the United Kingdom by virtue of the European Union (Withdrawal) Act 2018 (as amended). Upon the publication of this Announcement via the Regulatory Information Service, this inside information is now considered to be in the public domain.

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