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EEXI vs EEDI: What’s the Difference and Why It Matters

In recent years, the International Maritime Organization (IMO) has intensified its commitment to decarbonizing the global shipping industry. With maritime transport accounting for nearly 3% of global greenhouse gas (GHG) emissions, the IMO has introduced mandatory regulations to enhance the energy efficiency of ships. These initiatives aim to reduce the carbon footprint of the shipping sector and ensure it aligns with the targets set in the IMO’s Initial GHG Strategy, which includes a 40% reduction in carbon intensity by 2030 and a 50% reduction in overall GHG emissions by 2050, compared to 2008 levels.
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Two of the cornerstone regulations supporting this vision are the Energy Efficiency Design Index (EEDI) and the Energy Efficiency Existing Ship Index (EEXI). While both aim to improve energy efficiency and lower CO₂ emissions, they apply to different categories of vessels and involve distinct compliance strategies.

This article provides a detailed comparison of EEDI and EEXI, explains their respective scopes, calculation methods, and compliance requirements, and highlights why understanding the difference between the two is essential for shipowners, operators, and marine stakeholders worldwide.

1. What is EEDI?

The Energy Efficiency Design Index (EEDI) is a regulation introduced by the IMO to ensure that newly built ships are designed to be energy efficient. It was made mandatory for new ships of 400 gross tonnage (GT) and above under MARPOL Annex VI and came into force on January 1, 2013.

Applicability of EEDI

EEDI applies to:
  • New ships (built after January 1, 2013)
  • Ships ≥ 400 GT
  • Ship types including container ships, bulk carriers, tankers, gas carriers, general cargo ships, and passenger vessels

How is EEDI Calculated?

The EEDI is a quantitative measure of a ship’s CO₂ emissions relative to its transport work. It is calculated using the formula:
EEDI = (CO₂ emission from main + auxiliary engines + boilers) / (Transport work) Units: grams of CO₂ per tonne-nautical mile (g CO₂/ton-nm)
In simplified form:
EEDI = (Σ [Fuel consumption × CF]) / (Capacity × Speed)
Where:
  • Fuel consumption = Measured in tonnes/day
  • CF = Carbon emission factor for the specific fuel type
  • Capacity = Deadweight or gross tonnage depending on ship type
  • Speed = Design speed at 75% Maximum Continuous Rating (MCR)

Required and Attained Limits of EEDI

The EEDI regulation is implemented in phases:
  • Phase 0 (2013–2015): Reference level (baseline)
  • Phase 1 (2015–2020): 10% reduction from the reference line
  • Phase 2 (2020–2025): 20% reduction
  • Phase 3 (2025 onwards): Up to 30% reduction, depending on ship type
Each new vessel must demonstrate that its attained EEDI is less than or equal to the required EEDI threshold for compliance.

2. What is EEXI?

The Energy Efficiency Existing Ship Index (EEXI) is a recent IMO regulation that mirrors the EEDI but is designed for existing ships. Recognizing the large fleet of older vessels still in operation, the IMO introduced EEXI to ensure that these ships also contribute to global decarbonization goals.

Applicability of EEDI

  • Applies to ships ≥ 400 GT that fall under MARPOL Annex V
  • Entered into force on January 1, 2023
  • Targets existing ships that were not subject to EEDI requirements at the time of construction

Required and Attained Limits of EEXI

Similar to EEDI, EEXI also sets a required reduction target:
  • Reduction levels for EEXI are comparable to EEDI Phase 2 or 3, depending on the vessel type and size.
  • Each ship must calculate its attained EEXI and ensure it is less than or equal to the required EEXI to demonstrate compliance.

EEXI vs EEDI: Key Differences Table

Feature EEDI
(Energy Efficiency Design Index)		 EEXI
(Energy Efficiency Existing Ship Index)
Applies to Newly built ships constructed on or after January 1, 2013 Existing ships built before EEDI became mandatory
Year Implemented 2013, as part of IMO’s MARPOL Annex VI regulations 2023, under IMO’s short-term GHG reduction strategy
Focus Focuses on design efficiency of new ships during construction Focuses on bringing existing ships up to modern efficiency standards
Calculation Basis Measures CO₂ per ton-nautical mile using engine & design parameters Uses same formula as EEDI but applies it retrospectively
Compliance Strategy Design optimization via efficient hulls, engines, and ESDs Retrofitting, engine power limitation, operational measures

Why Does the eexi and eedi difference Matters?

Understanding the difference between EEDI and EEXI is vital for shipowners, operators, and fleet managers as it determines the compliance pathway for each vessel.

For new ships, compliance begins at the design stage, influencing decisions around propulsion, fuel, and hull form. In contrast, existing ships must undergo retrofitting, power limitation, or engine modifications to meet EEXI standards.

Financial Planning

EEDI involves upfront investment during the shipbuilding process, while EEXI often requires additional capital expenditure for retrofitting and operational changes, impacting older ships’ profitability.

Sustainability Goals

Both EEDI and EEXI are essential tools to help the maritime industry meet the IMO’s decarbonization targets. Together, they ensure that both new and legacy fleets contribute to reducing carbon emissions.

Regulatory Risk

Non-compliance with EEDI or EEXI can result in:
  • Detention at ports
  • Loss of charter opportunities
  • Reputational damage
  • Regulatory penalties or restrictions
In summary, both EEDI and EEXI are essential components of the IMO’s strategy to reduce carbon emissions from the maritime industry.
  • EEDI applies to new ships, requiring energy-efficient designs from the outset.
  • EEXI applies to existing ships, prompting retrofitting and operational adjustments.

Shipowners must carefully assess which regulation applies to each vessel in their fleet and take proactive steps to ensure compliance. Failure to comply not only risks regulatory penalties but also impacts long-term competitiveness and sustainability.

As the shipping industry navigates the journey to net-zero, staying ahead of regulatory standards is not just a requirement—it’s a strategic imperative.

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