As all we know, pollution is a serious actual problem that affects our society. Maritime transport is responsible of part of that pollution and with this purpose; measure to be taken in the logistical and maritime transport field is to reduce ships emissions. Air pollution is not the only problem, but greenhouse gas emissions too, mainly in the case of maritime transport pollutants as NOx and SOx gasses. This article tries to do a quick view on the last measures took by the International Maritime Organization (IMO) in order to reduce greenhouse gas emissions of shipping. An energy efficiency index for ships was created by the Marine Environment Protection Committee (MEPC) to improve their energy efficiency and then reduce fuel consumption. This index was developed in voluntary interim guidelines established in last sessions of the MEPC among 2009 and 2010, and can be applied to both new designs and ships in operation. Nowadays is just a voluntary measure that whatever ship-owner could take and verify, but until its approval there is for the moment no sanction if the results are not the expected ones by the guidelines. A description of the above mentioned guidelines will be exposed.