Traditionally, energy efficiency of ships is an area that has been subject to attention from charterers and shipowners. Operational energy efficiency is the sum of so many factors, pointing in different directions. How can anyone “reverse engineer” an observed operational energy efficiency of a ship to understand if it was good or bad? However, we should not forget that all parties share a common interest of optimal performance of the ships they build, operate and charter. These are fundamental aspects that the shipping industry struggles to get their heads around. Is it possible to observe a ship’s operational performance and from that determine if the Master did a good job? Is it possible from the observed operational efficiency of a ship to determine if it is the right one to charter? Ships’ performance has traditionally been referred to in charter contracts as warranties of speed and consumption at some defined loading condition. Such simplistic warranties have worked, probably because they are easy to understand and because it is similarly easy to determine if they are breached. The question if simple speed and consumption warranties are effective and are incentivizing a desired behavior amongst the decision makers in the industry could seem of less importance.