Rockhopper Regulatory News (RKH)

Embargoed: 0700hrs 20 April 2012

Rockhopper Exploration plc

("Rockhopper" or the "Company")

Revised CPR and Corporate Update

Rockhopper Exploration, the North Falkland Basin oil and gas company, is pleased to announce the publication of a Competent Person's Report ("CPR") prepared by Gaffney, Cline & Associates ("GCA").

CPR highlights

·; 355.6 MMbbls net to Rockhopper 2C contingent oil resources attributed to Sea Lion and adjacent discoveries

·; Sea Lion and adjacent discoveries estimated to have net to Rockhopper 2C risked NPV10 of US$ 4.1 billion and an unrisked NPV10 of US$ 4.7 billion

Resource and Economic Evaluation

The new CPR assigns a 90% chance of the Sea Lion field being progressed to successful development with the discoveries adjacent to Sea Lion assigned a 75% chance of development.

The probabilistic 1C, 2C and 3C resource numbers are based on low, best and high estimates of STOIIP of 0.65, 1.07 and 1.56 billion barrels respectively for the Sea Lion field. GCA has also indicated a deterministic best estimate STOIIP for the Sea Lion field of 1.3 billion barrels. The CPR also indicates significant additional prospectivity on licence PL032.

The new CPR contains the following table of resources net to Rockhopper. In arriving at the numbers below GCA used a probabilistic analysis with recovery factors ranging from 20 to 40 %.

The table below, extracted from the CPR, shows the Sea Lion risked and unrisked post tax net present value net to Rockhopper using a US$ 3/bbl discount to GCA's internal Brent oil pricing scenario and a 10 per cent discount rate.

Using the same assumptions the discoveries adjacent to Sea Lion are deemed to have risked and unrisked post tax net present value net to Rockhopper of:

Accordingly, Sea Lion and adjacent discoveries are estimated to have net to Rockhopper 2C risked NPV10 of US$ 4.1 billion and an unrisked NPV10 of US$ 4.7 billion

Field Development

The CPR also reports on a development concept for the Sea Lion field using a Floating Production Storage and Offloading vessel ("FPSO"). The principal assumptions of the development conceptinclude first oil being achieved at the start of 2016, with a plateau production rate 70,000 barrels per day for the first three years (based on the 2C scenario) and life-of-field development costs of $4.8 billion, based on a purchased new-build FPSO and inclusion of contingency. A breakdown of GCA's Capex is set out in the table below:

GCA has not provided an estimate of capital cost to achieve first oil production, however the Company's internal calculation of cost to first oil remains at approximately US$2 billion. This estimate is based on the Company's planned development of Sea Lion via a leased FPSO scenario, rather than the purchased new-build scenario assumed in GCA's costing, and a phased drilling programme.

The full CPR is available on the Company's website at www.rockhopperexploration.co.uk

Corporate Update

As previously announced the Company has prepared a data room to enable potential industry partners and debt providers access to the Sea Lion data. Collection and analysis of the field data is now complete and interested parties are actively reviewing the available information.

The Falkland Islands Government has recently clarified the position around the submission date for the Final Development Plan ("FDP") for the Sea Lion development. Whilst the licence issued to the Company states that a plan is to be submitted within three years of spudding the discovery well, the 2000 Model Clauses allow for five years if appraisal work has been undertaken. The Falkland Islands Government has therefore recently confirmed the final submission date for an FDP on Sea Lion is 15 April 2015. This does not change the Company's plans to develop Sea Lion as soon as practically possible.

Sam Moody, Chief Executive of Rockhopper, commented:

"We are delighted by the progression that the publication of today's CPR demonstrates as we continue to move forward our development for Sea Lion and nearby discoveries. We are particularly pleased by the results of the CPR due to the standing of consultants Gaffney, Cline & Associates Ltd and its reputation for thoroughness in the analysis of reservoir data and field development planning. The study has strongly reinforced our view of the potential of Sea Lion for commercial development."

Enquiries:

Rockhopper Exploration plc

Sam Moody - Chief Executive

Tel. +44 (0)20 7920 2340 (via M: Communications)

M: Communications

Patrick d'Ancona or Ben Simons

Tel. +44 (0)20 7920 2340

Canaccord Genuity Limited

Robert Finlay / Henry Fitzgerald-O'Connor

Tel. +44 (0) 20 7050 6500

Glossary of technical terms

Notes to Editors

Rockhopper was established in February 2004 with a strategy to invest in and carry out an offshore oil exploration programme to the north of the Falkland Islands. The Company floated on AIM in August 2005 and holds a 100 per cent. interest in four offshore production licences: PL023, PL024, PL032 and PL033 which cover approximately 3,800 sq. km. Rockhopper also farmed in (7.5% working interest) to licences PL003 and PL004, which are operated by Desire Petroleum. In addition to the original farm-in, and in consideration for drilling one well on the north-western acreage of licence PL004, known as Area 1, which contains the extension to the Sea Lion field as well as the Beverley, Casper and Casper South features, Rockhopper farmed-in with operatorship and an aggregate 60% interest in Area 1.

An extensive work programme has been carried out over a number of years on the licences operated by Rockhopper. This has included 2D and 3D Seismic and Controlled Source Electromagnetic Mapping (CSEM). In February 2010, the Ocean Guardian drilling rig arrived in Falkland waters to carry out a multi-well drilling campaign. Rockhopper drilled an exploration well on its Sea Lion prospect during April and May 2010, the result of which was the first oil discovery and Contingent Oil Resource in the North Falkland Basin. The Sea Lion discovery was successfully tested during September 2010 and June 2011 and was the first oil to flow to surface in Falkland Islands waters. Rockhopper's drilling campaign lasted from 16 April 2010 to 8 January 2012 and resulted in seven successful wells of the ten drilled, with three oil discoveries, three gas discoveries, multiple successful Sea Lion appraisal wells and a successful appraisal well on Casper.

Rockhopper Exploration plc www.rockhopperexploration.co.uk

NB: This statement has been approved by the Company's geological staff who include David Bodecott (Exploration Director), who is a Member of Petroleum Exploration Society of Great Britain (PESGB) and the American Association of Petroleum Geologists (AAPG) with over 30 years of experience in petroleum exploration and management, for the purpose of the Guidance Note for Mining, Oil and Gas Companies issued by the London Stock Exchange in respect of AIM companies, which outline standards of disclosure for mineral projects.