Proposed short-term measures to reduce the carbon intensity of international shipping fall into two categories: operational approaches and technical approaches. Based on the International Maritime Organization’s (IMO) latest “hybrid” proposal, ships will be required to adopt both approaches starting in 2023 to help meet IMO’s minimum 2030 carbon intensity goal. The proposed technical measure is Japan’s Energy Efficiency Existing Ship Index (EEXI), which would limit the amount of carbon dioxide (CO2) emitted per unit of transport supply. Main engine power limitation (EPL), a semi-permanent, overridable limit on a ship’s maximum power, is believed to be the easiest way for older ships to meet EEXI requirements. This paper assesses the effectiveness of the proposed Energy Efficiency Existing Ship Index (EEXI) as a means to reduce fuel use and carbon dioxide (CO2) emissions under the International Maritime Organization’s (IMO) initial greenhouse gas (GHG) strategy.