CEO [CNOOC] 424B2: (Original Filing)
[SUBJECT TO COMPLETION, DATED APRIL 20, 2018 PROSPECTUS SUPPLEMENT TO PROSPECTUS DATED APRIL 20, 2018 CNOOC FINANCE (2015) U.S.A. LLC (formed in the State of Delaware) US$ % Guaranteed Notes due 20 unconditionally and irrevocably guaranteed by CNOOC Limited (incorporated with limited liability in Hon]