Exhibit 8.1







Subsidiaries



As
of December 31, 2016, we owned, directly or indirectly, the following subsidiaries.



|Name
of entity                                       | Our
interest | Jurisdiction
of incorporation 
|---------------------------------------------------- | ------------ | ------------------------------
|CNOOC China Limited                                  | 100%         | Tianjin,
PRC                  
|CNOOC International
    Limited                      | 100%         | British
Virgin Islands        
|China
Offshore Oil (Singapore) International Pte Ltd | 100%         | Singapore                     
|CNOOC Finance (2003)
    Limited                     | 100%         | British
Virgin Islands        
|Malacca Petroleum Limited                            | 100%         | Bermuda                       
|OOGC America LLC                                     | 100%         | Delaware,
USA                 
|OOGC Malacca Limited                                 | 100%         | Bermuda                       
|CNOOC Southeast Asia
    Limited                     | 100%         | Bermuda                       
|CNOOC
    Africa Holding Ltd.                        | 100%         | British
Virgin Islands        
|CNOOC
    Africa Ltd.                                | 100%         | British
Virgin Islands        
|CNOOC
    Africa (UK) Limited                        | 100%         | London,
U.K.                  
|CNOOC SES Ltd.                                       | 100%         | Labuan,
F.T.,
        Malaysia
|CNOOC Poleng Ltd.                                    | 100%         | Labuan,
F.T.,
        Malaysia
|CNOOC Madura Ltd.                                    | 100%         | Labuan,
F.T.,
        Malaysia
|CNOOC NWS Private Limited                            | 100%         | Singapore                     
|CNOOC
    Australia E&P Pty Ltd                      | 100%         | Australia                     
|CNOOC Wiriagar Holding
    Limited                   | 100%         | British Virgin Islands        
|CNOOC
    Muturi Holding Limited                     | 100%         | British Virgin Islands        
|CNOOC Muturi Limited                                 | 100%         | The
Isle of Man               
|CNOOC
    Australia Limited                          | 100%         | British
Virgin Islands        
|CNOOC Exploration &
    Production Nigeria Limited   | 100%         | Nigeria                       
|CNOOC
    Hong Kong Holding Limited                  | 100%         | Hong
    Kong                 
|CNOOC
    Myanmar Holding Ltd.                       | 100%         | British
    Virgin Islands    





1






|CNOOC
    Myanmar Ltd.                                     | 100% | British
Virgin Islands        
|---------------------------------------------------------- | ---- | ------------------------------
|CNOOC
Middle East (Qatar) Limited                          | 100% | British
Virgin Islands        
|CNOOC Congo SA                                             | 100% | Republic
    of Congo         
|CNOOC Caspian (Kazakhstan)
    Ltd.                        | 100% | Cayman
    Islands            
|CNOOC Australia International
    Holdings Private Limited | 100% | Singapore                     
|CNOOC Australia Energy
    Capital Management Pty Ltd      | 100% | Australia                     
|CNOOC Batanghari Ltd.                                      | 100% | Labuan,
F.T.,
        Malaysia
|CNOOC Palung Aru Ltd.                                      | 100% | Labuan,
F.T.,
        Malaysia
|CNOOC FPSO Holding Limited                                 | 100% | Liberia                       
|CNOOC Liberia Limited                                      | 100% | Liberia                       
|CNOOC Uganda (BVI) Ltd                                     | 100% | British
    Virgin Islands    
|De coöperatieve
    vereniging CNOOC Netherlands U.A.      | 100% | The
    Netherlands           
|CNOOC Netherlands B.V.                                     | 100% | The
    Netherlands           
|CNOOC Uganda Ltd                                           | 100% | Uganda                        
|CNOOC
Deepwater Development Limited                        | 100% | Zhuhai,
PRC                   
|CNOOC Hainan Dock Limited                                  | 100% | Hainan,
PRC                   
|CNOOC Iraq Limited                                         | 100% | British
    Virgin Islands    
|CNOOC Finance (2011)
    Limited                           | 100% | British
    Virgin Islands    
|CNOOC
    Algeria (BVI) Limited                            | 100% | British
    Virgin Islands    
|CNOOC
    Reserves Fund I, Ltd.                            | 100% | Cayman
    Islands            
|CNOOC
    Luxembourg S.à r.l.                              | 100% | Luxembourg                    
|CNOOC
    Finance (2012) Limited                           | 100% | British
    Virgin Islands    
|CNOOC
    Finance (2013) Limited                           | 100% | British
    Virgin Islands    
|Tainan-Chaoshan
Petroleum Operating Company Limited*       | 50%  | British
    Virgin Islands    





2






|Husky - CNOOC Madura
    Limited *                                           | 40%  | British
Virgin Islands    
|---------------------------------------------------------------------------- | ---- | --------------------------
|Chaoyang Petroleum (BVI)
    Limited*                                        | 50%  | British
Virgin Islands    
|Chaoyang Petroleum (Trinidad)
    Block 3A Limited*                          | 50%  | Barbados                  
|Chaoyang Petroleum (Trinidad)
    Block 2C Limited*                          | 50%  | Barbados                  
|Bridas Corporation*                                                          | 50%  | British
    Virgin Islands
|Axion Energy Holding
    Ltd. *                                              | 50%  | British Virgin Islands    
|PNG Energy Limited                                                           | 70%  | British
    Virgin Islands
|GINI Energy Ltd                                                              | 70%  | Papua
    New Guinea      
|CNOOC Iceland ehf.                                                           | 100% | Iceland                   
|CNOOC
Luxembourg Holding S.à r.l.                                            | 100% | Luxembourg                
|CNOOC PETROLEUM BRASIL
    LTDA                                              | 100% | Brazil                    
|CNOOC International
    Energy Services (Beijing) Limited                    | 100% | Beijing,
    PRC          
|China Offshore Oil Corporation
    E&P Mexico, S.A.P.I. de C.V.              | 100% | Mexico                    
|China Offshore Oil Corporation
    Petroleum Mexico, S.A.P.I. de C.V.        | 100% | Mexico                    
|China
        Offshore Oil Corporation E&P Services Mexico, S.A.P.I. de C.V. | 100% | Mexico                    
|CNOOC New Zealand E&P
    Limited                                            | 100% | New
    Zealand           
|CNOOC
Finance (2015) Australia Pty Ltd                                       | 100% | Australia                 
|Aurora
Liquefied Natural Gas Ltd.                                            | 60%  | Alberta,
Canada           
|Canadian
Nexen Petroleum East Al Hajr Ltd.                                   | 100% | Alberta,
Canada           
|CanadianOxy
Offshore Production Co.                                          | 100% | Delaware,
USA             
|CNOOC Canada Energy
    Ltd.                                                 | 100% | British Columbia, Canada  
|CNOOC
Nexen Finance (2014) ULC                                               | 100% | Nova Scotia, Canada       





3






|CNOOC
Nexen Petroleum Guyana Limited        | 100% | Barbados                
|------------------------------------------- | ---- | ------------------------
|CNOOC UK Limited                            | 100% | England
and Wales       
|ICM Assurance Ltd.                          | 100% | Barbados                
|Nexen
Brasil Exploração Petróleo Ltda.      | 100% | Brazil                  
|Nexen
Energy Acquisitions Holdings Limited  | 100% | Jersey                  
|Nexen
Energy Capital Management U.S.A. Inc. | 100% | Delaware, USA           
|Nexen
Energy Holdings International Limited | 100% | Jersey                  
|Nexen
Energy Holdings U.S.A. Inc.           | 100% | Delaware,
USA           
|Nexen
Energy Marketing Europe Limited       | 100% | England
and Wales       
|Nexen
Energy Marketing U.S.A. Inc.          | 100% | Delaware,
USA           
|Nexen
Energy Services International Ltd.    | 100% | England
and Wales       
|Nexen
Energy Services U.S.A. Inc.           | 100% | Delaware,
USA           
|Nexen
Energy ULC                            | 100% | British
Columbia, Canada
|Nexen
Ettrick U.K. Limited                  | 100% | England
and Wales       
|Nexen
Holdings U.S.A. Inc.                  | 100% | Delaware,
USA           
|Nexen
Holdings West Africa Limited          | 100% | Jersey                  
|Nexen
New Venture Jersey Limited            | 100% | Jersey                  
|Nexen
No. 8 Ltd.                            | 100% | Alberta,
Canada         
|Nexen
Oil & Gas Holdings U.S.A. Inc.        | 100% | Delaware,
USA           
|Nexen
Oilfield Services Nigeria Limited     | 100% | Jersey                  





4






|Nexen
Petroleum Colombia Limited                           | 100% | Jersey              
|---------------------------------------------------------- | ---- | --------------------
|Nexen
Petroleum Deepwater Nigeria Limited                  | 100% | Nigeria             
|Nexen
Petroleum Dragon U.K. Limited                        | 100% | England
and Wales   
|Nexen
Petroleum Exploration and Production Nigeria Limited | 100% | Nigeria             
|Nexen
Petroleum Nigeria Limited                            | 100% | Nigeria             
|Nexen
Petroleum Offshore U.S.A. Inc.                       | 100% | Delaware,
USA       
|Nexen
Petroleum Operations Yemen Limited                   | 100% | Jersey              
|Nexen
Petroleum Poland Sp. zo.o.                           | 100% | Poland              
|Nexen
Petroleum Sales U.S.A. Inc.                          | 100% | Texas,
USA          
|Nexen
Petroleum U.K. Holdings Limited                      | 100% | England
and Wales   
|Nexen
Petroleum U.K. Limited                               | 100% | England
and Wales   
|Nexen Petroleum U.S.A.
    Inc.                            | 100% | Delaware,
USA       
|Nexen
Resource Holdings U.K. Limited                       | 100% | England
and Wales   
|Wascana Energy 2001
    Ltd.                               | 100% | Saskatchewan,
Canada
|Canadian Nexen Petroleum
    Yemen                         | 100% | Alberta,
Canada     
|Nexen Crossfield Partnership                               | 100% | Alberta,
Canada     
|Nexen Marketing                                            | 100% | Alberta,
Canada     
|Nexen Med Hat-Hatton
    Partnership                       | 100% | Alberta,
Canada     
|Nexen
Nigerian Holdings Coöperatief U.A                    | 100% | The
Netherlands     
|Nexen Oil Sands Partnership                                | 100% | Alberta,
Canada     
|CNOOC Finance (2015)
    U.S.A. LLC                        | 100% | Delaware, USA       



*We
and our partners jointly control these entities.







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