The oil and gas industry is usually related to environmental problems and high level of CO2 emission. This work aims to evaluate different cogeneration plants usually used in FPSOs using cold deep sea water to improve efficiency of the cogeneration plants. Petroleum production data from a given well is used to size process plant while cogeneration plants are modeled using electrical and thermal demands required by process plant. Off-design operation caused by variation in utilities demand is also considered. Optimization using the GRG (Generalized Reduced Gradient) method is performed to minimize fuel consumption by selecting the best load distribution among equipment yearly. Results reveal that the additional cooling subsystem using deep sea water increases the exergy efficiency in 2.5% for gas turbines (which is the most usual technology) and as a consequence, a reduction of 128585 tin CO2 emissions was noticed. For the steam plant, the increase in exergy efficiency was 2.9%. For reciprocating engine and combined cycle technologies there is no significant benefit. Reciprocating engines plant presented the highest exergy efficiency (similar to 50%), even though no benefits from the use of the additional cooling system were achieved for this technology. (C) 2019 Elsevier Ltd. All rights reserved.