Further to the announcement released by Northern on 23 May 2009, the Board of Northern is pleased to announce that the acquisition of ATI has become effective and trading in the new Northern Shares is expected to begin at 8.00 a.m. on 25 June 2009.

The latest date for despatch of New Northern Share certificates and crediting of CREST accounts under the Scheme will be 8 July 2009. In accordance with the Scheme, a total of 7,418,480 New Northern Shares will be issued to Scheme Shareholders on the register at 6.00 p.m. on 22 June 2009. In addition, pursuant to the proposals made in the Warrantholder Circular dated 28 April 2009, 279,787 New Northern Shares and 408,750 new warrants over shares in the capital of Northern will be issued to former ATI Warrantholders.

ATI will be withdrawn from trading on PLUS at 16.30 p.m. today.

Terms and expressions used in this announcement shall have the same meanings given to them in the announcements released by Northern on 3 April 2009 and 29 April 2009.

For further information please contact:

Northern Petroleum Plc
Tel: +44 (0) 20 7469 2900
Richard Latham, Chairman
Graham Heard, Exploration & Technical Director

Investec (Financial Adviser)
Tel: +44 (0) 20 7597 5000
Michael Ansell / Patrick Robb / Avital Lobel

ATI Oil Plc
Tel: +44 (0) 20 7469 2940
Per Gunnar Loge, Chief Executive Officer

KBR (Financial adviser to ATI)
Tel: +44 (0) 20 3100 8300
Hugh Oram

The directors of Northern accept responsibility for the information contained in this announcement. To the best of the knowledge and belief of the directors of Northern (having taken all reasonable care to ensure that such is the case) the information contained in this announcement is in accordance with the facts and does not omit anything likely to affect the import of such information.

This announcement will shortly be published in accordance with Rule 19.11 of the Takeover Code on Northern’s website, http://www.northpet.com, in the news section.

Dealing Disclosure Requirements

Under the provisions of Rule 8.3 of the Takeover Code, if any person is, or becomes, 'interested' (directly or indirectly) in 1% or more of any class of 'relevant securities' of the Company or ATI, all 'dealings' in any 'relevant securities' of that company (including by means of an option in respect of, or a derivative referenced to, any such 'relevant securities') must be publicly disclosed by no later than 3.30 pm (London time) on the London business day following the date of the relevant transaction. This requirement will continue until the date on which the offer becomes, or is declared, unconditional as to acceptances, lapses or is otherwise withdrawn or on which the 'offer period' otherwise ends. If two or more persons act together pursuant to an agreement or understanding, whether formal or informal, to acquire an 'interest' in 'relevant securities' of the Company or ATI, they will be deemed to be a single person for the purpose of Rule 8.3.

Under the provisions of Rule 8.1 of the Takeover Code, all 'dealings' in 'relevant securities' of the Company or ATI by the Company or ATI, or by any of their respective 'associates', must be disclosed by no later than 12.00 noon (London time) on the London business day following the date of the relevant transaction.

A disclosure table, giving details of the companies in whose 'relevant securities' 'dealings' should be disclosed, and the number of such securities in issue, can be found on the Takeover Panel's website at www.thetakeoverpanel.org.uk.

'Interests in securities' arise, in summary, when a person has long economic exposure, whether conditional or absolute, to changes in the price of securities. In particular, a person will be treated as having an 'interest' by virtue of the ownership or control of securities, or by virtue of any option in respect of, or derivative referenced to, securities.

Terms in quotation marks are defined in the Takeover Code, which can also be found on the Panel's website. If you are in any doubt as to whether or not you are required to disclose a 'dealing' under Rule 8, you should consult the Panel.

Investec Investment Banking, a division of Investec Bank plc ("Investec"), which is authorised and regulated in the United Kingdom by the FSA, is acting for Northern and for no-one else in connection with the Proposals and the matters referred to in this announcement and will not be responsible to anyone other than Northern for providing the protections afforded to customers of Investec or for providing advice in connection with the matters set out in this announcement.