Energy efficiency has emerged as a key point in port industry because of different factors such as the adoption of stronger environmental regulations and the increasing pressure of the local community on the surrounding ports. As gathering operational data from port terminals can be difficult due to privacy, studies on emissions and energy efficiency of these terminals are scarce. The following research provides key information about the real energy consumption and CO2 emissions of one of the most relevant container terminals in the Mediterranean area, located in Valencia, Spain. The results show that yard terminal tractors and rubber tyred gantry cranes (RTGs) are the main emission sources, accounting for 68.1% of the terminal's total CO2 emissions. After identifying the equipment responsible for the environmental problem, two solutions aimed at improving the energy efficiency of the terminal have been studied: the retrofitting of RTGs cranes and the replacement of terminal tractors powered by fuel for a new liquefied natural gas tractor, which contributed to a large reduction of CO2 emissions. Additionally, the present research explores the different policies at the disposal of port authorities in order to foster the implementation of solutions aimed at mitigating the environmental externalities by terminal operators.