This study presents an overview of emission control based energy efficiency measures in the ship operation phase with respect to possible energy conservation situations. The first part of the study discusses energy efficiency measures under the respective emission control regulations in the shipping industry. That illustrates the emission control concepts of Emission Control Areas (ECAs), CO2 reductions, SOx limits, and NOx Technical Codes and the energy efficiency concepts of Energy Efficiency Design Index (EEDI), Energy Efficiency Operational Indicator (EEOI), and Ship Energy Efficiency Management Plan (SEEMP). The second part consists of identifying the possible situations of energy conservation at the ship operation phase with respect to the proposed energy flow path (i.e. marine power plant, engine propeller interactions, and ship resistance). Initial data analyses of performance and navigation parameters are for a selected vessel presented to support the above situations along the energy flow path. High power consumption regions identified and potential energy conservation situations with respect to the EEOI presented are an important part of the SEEMP. Finally, under these results the possibilities of using appropriate navigation strategies (i.e. voyage planning, and draft and trim optimization) especially in the designated ECAs to reduce exhaust emissions (i.e. CO2, SOx and NOx) are also discussed.