CEO [CNOOC] 424B2: (Original Filing)
[SUBJECT TO COMPLETION, DATED May 1, 2013 Registration No. 333-188261 Registration No. 333-188261-01 PROSPECTUS SUPPLEMENT TO PROSPECTUS DATED May 1, 2013 CNOOC Finance (2013) Limited (incorporated with limited liability in the British Virgin Islands) US$ % Guaranteed Notes due 2016 US$ % Guaranteed Notes due 2018 US$ % Guaranteed Notes due 2023 US$ % Guaranteed Notes due 2043 unconditionally and]