The implementation of the CII has driven an increased awareness of operational efficiency and provided a standardized framework for operational energy efficiency. Optimizing the CII rating of a vessel is challenging, requiring transparent collaboration among multiple stakeholders (shipowner, operator, charterers, technical managers, and ports and terminals). Because of this complexity, improvements in CII ratings are expected to initially come from operational measures such as speed reduction and vessel deployment changes, with the adoption of technical efficiency measures being limited. This effect is amplified by the operational nature of the CII rating, which means that two sister vessels deployed in different trades can very easily have different CII ratings.