2 April 2026

Rockhopper Exploration plc

("Rockhopper" or the "Company")

Sea Lion Independent Recoverable Reserves and Resources Evaluation

Rockhopper Exploration plc (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 "Report"). The Report is effective as at 31 December 2025.

The Report shows that overall gross resource volumes are consistent with the Company's previous independent resource evaluation, also conducted by NSAI, dated June 2025 (the "June 2025 Report").

Importantly, the Report has reclassified volumes contained in the Sea Lion Field Northern Development Area ("NDA") Phases 1 and 2 from the Contingent Resources classification to the Reserves classification. This reclassification has been possible following the Company's Final Investment Decision ("FID") on the Sea Lion field, made in December 2025. Phase 2 of the Sea Lion development is expected to be financed from cashflow generated by Phase 1. Later phases of the Sea Lion development have remained within the Contingent Resources category.

Following completion of the placing, the Company had, as at 31 December 2025, a cash balance of approximately US$179 million (unaudited) which is anticipated to be sufficient to fund Rockhopper's proportion of the capex required for the Phase 1 development plan for the Sea Lion field.

Key Information (oil only)

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.

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)

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

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.

Economic Parameters

The 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:

The development scenario underlying the NPV calculation for the contingent resources aligns with the previously disclosed multi-phase, two-FPSO scheme comprising the Northern Development Area ("NDA") Phases 1, 2 and 3 and the Central Development Area ("CDA") Phases 1 and 2.

Bluewater, the FPSO operator, has served notice on the Aoka Mizu FPSO and the vessel is expected to leave its current location in mid-2026 ahead of a period of refurbishment work prior to deployment at Sea Lion.

Sam Moody, Chief Executive Officer of Rockhopper, commented:

"We are delighted to book in excess of 100 million barrels of 2P reserves following the sanction of Sea Lion Phase 1 - another milestone for Rockhopper. The new NSAI report independently confirms the significant value we are now on the path to unlocking. Navitas, our Operator, has recently reported good progress on the project and has reiterated its target for first oil in early 2028."

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 Report also includes economic analysis under Low and High Price Case sensitivities.

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

Resource Disclosure

The 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.

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