This Master's thesis conducts a multi-criteria analysis of ship energy efficiency measures, and especially for Steam Turbine Liquefied Natural Gas (LNG) carriers, focusing on both technical and environmental implications. By evaluating a range of energy efficiency measures, including technological innovations and operational strategies, the study aims to identify the most cost-effective approaches to reduce greenhouse gas emissions and enhance operational efficiency. The research employs a multi-criteria decision-making framework to balance environmental benefits with economic feasibility, considering the unique characteristics of LNG carriers of various ages. Findings reveal that certain energy efficiency measures offer significant advantages in reducing environmental impact and operational costs, though their effectiveness varies by ship size and design. The thesis emphasizes the need for a tailored approach in implementing energy efficiency solutions, highlighting the importance of industry-wide collaboration to achieve sustainability goals in the maritime sector.