Re: Holding in Company

Tullow Oil PLC
07 June 2005


SCHEDULE 10

NOTIFICATION OF MAJOR INTERESTS IN SHARES


1. Name of company

Tullow Oil plc


2. Name of shareholder having a major interest

Columbia Wanger Asset Management,L.P.


3. Please state whether notification indicates that it is in respect of holding of the shareholder named in 2 above or 
in respect of a non-beneficial interest or in the case of an individual holder if it is a holding of that person's 
spouse or children under the age of 18

See 4 below


4. Name of the registered holder(s) and, if more than one holder, the number of shares held by each of them

Columbia Acorn Fund - State Street Nominees Ltd. 15,400,000 shares
Columbia Acorn International Fund - State Street Nominees Ltd. 6,500,000 shares
AXP Partners International Aggressive Growth Fund - Bank of New York Nominees Ltd. 443,000 shares
Wanger European Small Cap Fund - State Street Nominees Ltd. 406,900 shares
Wanger International Small Cap Advisor- State Street Nominees Ltd. 1,700,000 shares
Oregon State Treasury - State Street Nominees Ltd. 2,500,000 shares
Fairfax County Employee Retirement Fund-Mellon Bank Nominees Ltd. 370,000 shares

5. Number of shares / amount of stock acquired

Not disclosed

6. Percentage of issued class

Not Disclosed

7. Number of shares / amount of stock disposed

Not Disclosed

8. Percentage of issued class

Not Disclosed

9. Class of security

Ordinary 10p shares

10. Date of transaction

-

11. Date company informed

6 June 2005

12. Total holding following this notification

 27,319,900

13. Total percentage holding of issued class following this notification

4.22%

14. Any additional information

Total shares in issue 646,502,128


15. Name of contact and telephone number for queries

Tom Hickey 0207 333 6800


16. Name and signature of authorised company official responsible for making this notification

Tom Hickey

Date of notification
7 June 2005



This announcement has been issued through the Companies Announcement Service of

                           the Irish Stock Exchange.







                      This information is provided by RNS
            The company news service from the London Stock Exchange