RIO DE JANEIRO, Dec 30 (Reuters) - Brazilian state-run oil company Petrobras has declared four offshore concessions in the states of Alagoas and Sergipe commercially viable in presentations to the nation's oil regulator, it said in securities filing on Thursday.

The company has proposed installing two major oil platforms known as FPSOs in the region, said the firm, formally known as Petroleo Brasileiro SA. (Reporting by Gram Slattery Editing by Chris Reese)