CSEM Survey Prelim Report

Rockhopper Exploration plc
28 June 2006


PRESS RELEASE

For immediate release: 28 June 2006


                  Electromagnetic Surveys:- Preliminary Report

Rockhopper Exploration plc ('Rockhopper' or 'the Company') is pleased to
announce that preliminary results from the Controlled Source Electromagnetic
(CSEM) survey data suggests that resistive bodies co-incident with the mapped
structures are present. Such resistive features, when combined with seismic data
and other technical studies, can be positive indicators of the presence of
hydrocarbons.

Background

Rockhopper contracted Offshore Hydrocarbon Mapping plc in January 2006 to
conduct two CSEM surveys over its acreage in the North Falkland Basin during
January and February 2006. The surveys covered prospect J1 and lead K. Those
areas were also the subject of a new 2D seismic survey, also acquired during
January and February 2006.


Both targets (J1 and K) are located in relatively shallow water of less than
200m in licences PL023 and PL024, an undrilled part of the North Falkland Basin
near the Islands representing an independent play type from those plays and
targets in the more northern part of the basin. The targets are both relatively
shallow and this, combined with the shallow water depth, would make any wells
drilled relatively quick and inexpensive should a rig be drilling in the area.

CSEM Preliminary Results

The preliminary results of both surveys have indicated the presence of discreet
resistors in the area of the targets which, when combined with the existing
seismic data, could prove to be a positive indicator of hydrocarbons.

The Directors remain cautious until the next step is complete, which will be to
fully integrate the CSEM results with the new seismic data, which is in the
final stages of data processing. Once this is complete, the Company should have
a more definitive view of the extent of any potential reservoirs. That process
could take several months.

Should the integration confirm the robust physical nature of J1 and support the
interpretation of the resistor as a possible hydrocarbon accumulation, that
target could be moved to the status of a fully drillable prospect without the
need to acquire any additional seismic, subject to all necessary regulatory
consents.

At the time of the Rockhopper Exploration AIM IPO in August 2005, Scott
Pickford, the independent consultants, estimated that the J1 prospect had a P50
of approximately 328 million barrels STOIIP. Lead K was not assessed by Scott
Pickford, but currently has a maximum mapped closure of approximately 29 km2.

Samuel Moody, Managing Director commented:

'While the report from OHM is preliminary and further integration with the new
2D seismic is required, we are greatly encouraged by these initial indications.
This represents a truly significant step forward in the development of licences
PL023 and PL024 as we now have corroborating signs of potential hydrocarbons in
both the seismic data and the CSEM.'

'The CSEM surveys are specific to the targets covered and it's therefore
difficult to infer anything from these preliminary indications from J1 and K in
relation to the rest of the basin as a whole. However, it does give us
encouragement that the southern part of the basin is as prospective as the
geologically different central and northern parts, in which we also have
interests and are actively exploring.'


NB: This statement has been approved by the Company's geological staff who
include Keith Williams (Exploration Director), who is a Member of The European
Association of Geoscientists & Engineers (EAGE) 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.


For further information, please contact:

Rockhopper Exploration plc www.rockhopperexploration.co.uk
Sam Moody - Managing Director 01722 414 419

Aquila Financial Ltd (PR) www.aquila-financial.com
Peter Reilly 020 7202 2601
Yvonne Fraser 020 7202 2609

Teather & Greenwood (NOMAD & Broker) www.teathers.com
James Maxwell (Corporate Finance) 020 7426 9000
Tanya Clarke (Specialist Sales)


Notes to editors
A graphic showing the location of licences PL023 and PL024, the J1 prospect and
other leads, the 2006 2D seismic and CSEM survey locations and the existing 2D
seismic data to which Rockhopper has access is available from Aquila Financial
Limited or can be downloaded from the Rockhopper website:

www.rockhopperexploration.co.uk

The Rockhopper Group started trading in February 2004 to invest in and carry out
an offshore oil exploration programme to the north of the Falkland Islands. The
Group, floated on AIM in August 2005, is currently the largest licence holder in
the North Falkland Basin and has a 100 per cent. interest in four offshore
production licences which cover approximately 5,800 sq. km. These licences have
been granted by the Falkland Islands government.

About Offshore Hydrocarbon Mapping plc
www.ohmsurveys.com

Offshore Hydrocarbon Mapping plc, listed on London's Alternative Investment
Market in March 2004 (OHM).

OHM's survey method transmits an electromagnetic field into the earth, which is
modified by the presence of subsurface resistive layers. These changes in the
field are measured and the resulting data is processed to provide information on
the resistive structure of the subsurface.

Because hydrocarbon accumulations are generally very resistive, this method can
indicate the presence of oil and gas in water depths of as little as 50 metres
in certain circumstances, and can detect and map the edges of such
accumulations. This reduces the risk of drilling non-commercial exploration
wells and can reduce the need for appraisal drilling, thereby creating
considerable value for oil explorers.


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