29.04.09

NORTHERN PETROLEUM PLC POSTING OF SCHEME CIRCULAR

NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION IN WHOLE OR IN PART IN, INTO OR FROM ANY JURISDICTION WHERE TO DO SO WOULD CONSTITUTE A VIOLATION OF THE RELEVANT LAWS OF SUCH JURISDICTION

Recommended Proposals for the acquisition of ATI Oil plc by Northern Petroleum plc to be effected by way of a Scheme of Arrangement under Part 26 of the Companies Act 2006

On 3 April 2009, the Independent Northern Directors and the Independent ATI Directors announced that they had reached agreement on the terms of a recommended acquisition by members of the Northern Group of the entire issued and to be issued share capital of ATI not already owned by Northern, to be implemented by means of a court-sanctioned scheme of arrangement under Part 26 of the Companies Act 2006, which will include the Capital Reduction (the "Scheme").

The Independent Northern Directors and the Independent ATI Directors are pleased to announce that the Circular, which sets out, amongst other things, the full terms and conditions of the Proposals and an explanatory statement, together with the action to be taken by Scheme Shareholders, was posted to holders of ATI Shares on 28 April 2009 outside normal business hours. Notices convening the Court Meeting and the General Meeting are contained in the Circular. The Court Meeting will start at 11.00am and the General Meeting will start at 11:15 am (or as soon thereafter as the preceding Court Meeting has been concluded or adjourned) on 28 May 2009 at Martin House, 5 Martin Lane, London EC4R 0DP. Subject to the satisfaction or waiver of the conditions of the Proposals, it is currently expected that the Proposals will become effective on 24 June 2009. If any of the expected dates change, Northern will give adequate notice of the change by issuing an announcement through a Regulatory Information Service.

Copies of the Circular are displayed on the Northern website http://www.northpet.com and are also available for inspection at the offices of Berwin Leighton Paisner LLP at Adelaide House, London Bridge, London EC4R 9HA.

A circular to ATI Warrantholders (the “Warrantholder Circular”) was also posted on 28 April 2009 outside normal business hours containing certain proposals to ATI Warrantholders in connection with the Scheme. A notice convening a meeting of ATI Warrantholders, at which an extraordinary resolution (the “Extraordinary Resolution”) is proposed to seek ATI Warrantholders’ consent (a) to the Capital Reduction and (b) to certain changes to the terms of the ATI Warrants, is set out in an appendix to the Warrantholder Circular.

Northern has received, in aggregate, irrevocable commitments to vote in favour of the Extraordinary Resolution in respect of 5,160,000 ATI Warrants, representing approximately 70.6 per cent. of the ATI Shares attributable to the ATI Warrants currently in issue.

Terms and expressions used in this announcement shall, unless the context otherwise requires, have the same meanings as given to them in the announcement of 3 April 2009.

Download the Circular to ATI Shareholders (PDF)

Download the Circular to ATI Warrantholders (PDF)

Enquiries:

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

Investec (financial adviser to Northern)
Michael Ansell Patrick Robb Avital Lobel
Tel: +44 (0)20 7597 5000

Buchanan Communications (Analysts)
Tim Thompson / Ben Romney
Tel: +44 (0)20 7466 5000

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

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

This announcement is not intended to be and does not constitute, or form part of, any offer to sell or invitation to purchase, otherwise acquire, subscribe for, sell or otherwise dispose of, any securities or the solicitation of any vote or approval in any jurisdiction pursuant to the Proposals or otherwise, nor shall there by any sale, issue or transfer of the securities referred to in this announcement in or into any jurisdiction in contravention of any applicable law. The Proposals will be made solely through the Circular, which will contain the full terms and conditions of the Proposals, including details of how to vote in respect of the Proposals. Scheme Shareholders are advised to read carefully the formal documentation in relation to the Proposals, once it is dispatched. Any acceptance or other response to the Proposals should be made only on the basis of the information in the Circular. In deciding whether or not to approve the Scheme, Scheme Shareholders must rely solely on the terms and conditions of the Proposals and the information contained, and the procedures described, in the Circular.

The directors of Northern accepts responsibility for the information contained in this announcement, except for the information in this announcement relating to ATI, the directors of ATI and their close relatives and related trusts and other Interested Persons (as defined below) and persons acting in concert with, and associates of, ATI. Subject to the foregoing, to the best of the knowledge and belief of the directors of Northern (who have taken all reasonable care to ensure that such is the case), the information contained in this announcement for which they are responsible is in accordance with the facts and does not omit anything likely to affect the import of that information.

The directors of ATI accept responsibility for the information contained in this document concerning ATI, themselves and their close relatives and related trusts and other Interested Persons (as defined below) and persons acting in concert with, and associates of, ATI. To the best of the knowledge and belief of the directors of ATI (who have taken all reasonable care to ensure that such is the case), the information contained in this announcement for which they are responsible is in accordance with the facts and does not omit anything likely to affect the import of that information.

The Independent ATI Directors each accept responsibility for any opinion attributed to the Independent ATI Directors contained in this announcement, including the unanimous intention to recommend the Proposals.

Investec, which is authorised and regulated in the UK by the FSA, is acting exclusively as financial adviser to Northern in relation to the Proposals and the matters referred to in this announcement and is not acting for any other person in connection with the Proposals and will not be responsible to anyone other than Northern for providing the protections afforded to clients of Investec or for providing advice in relation to the Proposals or any other matters referred to in this announcement.

KBR which is authorised and regulated in the UK by the FSA, is acting exclusively as financial adviser to ATI and no-one else in connection with the Proposals and the matters referred to in this announcement and is not acting for any other person in connection with the Proposals and will not be responsible to anyone other than ATI for providing the protections afforded to clients of KBR or for providing advice in relation to the Proposals or any other matters referred to in this announcement.

This announcement has been prepared for the purpose of complying with English law and the Takeover Code, and the information disclosed may not be the same as that which would have been disclosed if this announcement had been prepared in accordance with the laws of jurisdictions outside the UK.

Any person (including, without limitation, any custodian, nominee and trustee) who would, or otherwise intends to, or who may have a contractual or legal obligation to, forward this announcement and/or the Circular and/or any other related document to any jurisdiction outside the UK should inform themselves of, and observe, any applicable legal or regulatory requirements of their jurisdiction before taking any action.

FORWARD LOOKING STATEMENTS

This announcement, including information included or incorporated by reference in this announcement, may contain "forward-looking statements" concerning Northern and ATI. These forward-looking statements can be identified by the fact that they do not relate only to historical or current facts. Generally, the words "will", "may", "should", "continue", "believes", "expects", "intends", "anticipates”, “plan”, “projects”, “forecast”, “estimate” or similar expressions identify forward-looking statements. The forward-looking statements involve risks and uncertainties that could cause actual results to differ materially from those expressed in the forward-looking statements. Many of these risks and uncertainties relate to factors that are beyond the companies' abilities to control or estimate precisely, such as future market conditions and the behaviours of other market participants, and therefore undue reliance should not be placed on such statements. Northern and ATI assume no obligation and do not intend to update these forward-looking statements, except as required pursuant to applicable law.

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 per cent. or more of any class of "relevant securities" of Northern 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 p.m. (London time) on the business day following the date of the relevant transaction. This requirement will continue until the date on which the Proposals become effective, lapse or are 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 Northern 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 ATI or Northern by ATI or Northern, 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.

OVERSEAS TERRITORIES

The distribution of this announcement in jurisdictions other than England and Wales may be restricted by law and therefore any persons who are subject to the laws of any jurisdiction other than England and Wales should inform themselves about, and observe, any applicable requirements. In particular, no offer will be made, directly or indirectly, in or into, or by use of the mails of, or by any means or instrumentality (including, without limitation, facsimile transmission, internet, email, telex or telephone) of interstate or foreign commerce of, or any facility of a national state or other securities exchange of a Prohibited Territory and subject to certain exceptions no offer will be capable of acceptance by any such use, means instrumentality or facility from within any Prohibited Territories. Copies of this announcement and any related offer documentation are not being, will not be, and must not be, mailed or otherwise distributed or sent in or into any Prohibited Territory.

This announcement is not intended to, and does not, constitute or form any part of an offer to sell or an invitation to purchase or subscribe for any securities or the solicitation of an offer to buy or subscribe for any securities nor shall there be any sale, issuance or transfer of the securities referred to in the announcement in the United States or any jurisdiction in contravention of applicable law.

The New Northern Shares have not been, and will not be, registered under the US Securities Act of 1933, as amended (the "Securities Act"), or under the securities laws of any state, district, province or other jurisdiction of the United States, Canada, Australia, the Republic of South Africa, the Republic of Ireland, Japan or any other Prohibited Territory. No regulatory clearances in respect of the New Northern Shares have been, or will be, applied for in any state, province, territory or jurisdiction other than the United Kingdom. Accordingly, unless an exemption under relevant securities laws is applicable, the New Northern Shares are not being, and may not be, offered, sold, resold, delivered, distributed or otherwise transferred, directly or indirectly, in or into any Prohibited Territory or to or for the account or benefit of any resident of a Prohibited Territory.

The availability of an offer to Scheme Shareholders who are not resident in, and citizens of, the United Kingdom may be affected by the laws of the relevant jurisdictions in which they are located or of which they are citizens. Such persons should inform themselves of, and observe, any applicable legal or regulatory requirements of their jurisdictions. Further details in relation to overseas shareholders will be contained in the Circular.

This announcement has been prepared for the purpose of complying with English law and the Takeover Code and the information disclosed may not be the same as that which would have been disclosed if this announcement had been prepared in accordance with the laws of jurisdictions outside England and Wales.