Holding(s) in Company

For filings with the FCA include the annex

For filings with issuer exclude the annex

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARES

1. Identity of the issuer or the underlying issuerof existing shares to which voting rights areattached:

Tullow Oil plc

2 Reason for the notification (please tick the appropriate box or boxes):

An acquisition or disposal of voting rights

X

An acquisition or disposal of qualifying financial instruments which may result in the acquisition of shares already issued to which voting rights are attached

An acquisition or disposal of instruments with similar economic effect to qualifying financial instruments

An event changing the breakdown of voting rights

Other (please specify):

3. Full name of person(s) subject to thenotification obligation:

OppenheimerFunds, Inc

4. Full name of shareholder(s)  (if different from 3.):

5. Date of the transaction and date onwhich the threshold is crossed orreached:

02 June 2015

6. Date on which issuer notified:

03 June 2015

7. Threshold(s) that is/are crossed orreached:

5.00% (decreased to 4.96%)

8. Notified details:

Investor Relations Contact:

Tullow Oil plc

9 Chiswick Park

566 Chiswick High Road

London W4 5XT

United Kingdom

[email protected]

A: Voting rights attached to shares

Class/type ofshares

if possible usingthe ISIN CODE

Situation previousto the triggeringtransaction

Resulting situation after the triggering transaction

NumberofShares

NumberofVotingRights

Numberof shares

Number of votingrights

% of voting rights

Direct

Direct

Indirect

Direct

Indirect

GB0001500809

46,820,017

46,820,017

45,191,459

45,191,459

4.96%

B: Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Expirationdate

Exercise/Conversion Period

Number of votingrights that may beacquired if theinstrument isexercised/ converted.

% of votingrights

C: Financial Instruments with similar economic effect to Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Exercise price

Expiration date

Exercise/Conversion period

Number of voting rights instrument refers to

% of voting rights

Nominal

Delta

Total (A+B+C)

Number of voting rights

Percentage of voting rights

45,191,459

4.96%

9. Chain of controlled undertakings through which the voting rights and/or thefinancial instruments are effectively held, if applicable:

OppenheimerFunds ("OFI") is a registered inivestment advisor with the US SEC. Its ultimate parent company, Massachusetts Mutual Life Insurance Company, qualifies for disaggregation under FSA regulations. The shares of the issuer are held by investment accounts managed by OFI and its subsidiary, OFI Global Asset Management

Proxy Voting:

10. Name of the proxy holder:

11. Number of voting rights proxy holder will ceaseto hold:

12. Date on which proxy holder will cease to holdvoting rights:

13. Additional information:

14. Contact name:

Cathy Swegart

Sr Compliance Specialist

OppenheimerFunds Inc

15. Contact telephone number:

001 (303) 768-3149