Environmental Ship Index (ESI): The Complete Guide for Shipping Companies and Ports

As emissions regulations tighten and sustainability expectations increase, shipping companies and ports are looking for ways to link environmental performance with commercial outcomes. The Environmental Ship Index (ESI) provides a structured framework that allows ports to reward ships performing beyond regulatory emission standards. Through ESI, environmental performance can translate directly into port fee discounts and operational incentives. 

The Environmental Ship Index was developed by the port community through the International Association of Ports and Harbors (IAPH) to provide a transparent and globally harmonised way to recognise ships that perform better than regulatory environmental standards. Today, the Environmental Ship Index has become the world’s leading port incentive scheme, with over 6,800 ships and more than one hundred ports participating globally. 

Environmental Ship Index Definition

The Environmental Ship Index (ESI) assigns environmental performance scores to ships, enabling ports to grant incentives such as port fee discounts. Participating ports act as Incentive Providers, while ships registered in the index are considered Incentive Receivers. 

Environmental Ship Index at a Glance

• Launched: 2011

• Participating ports: 100+ worldwide

• Registered vessels: 6,800+

• Governance: Backed by the International Association of Ports and Harbours (IAPH)

• Ownership: ESI Foundation

• Administration: OceanScore

• Recognition: Recognised by the International Maritime Organization (IMO) 

Why the Environmental Ship Index Was Created

Ports play a central role in reducing emissions from maritime transport. However, ports do not directly control vessel technologies or operational decisions. The Environmental Ship Index was created to bridge this gap. 

Rather than imposing new regulatory requirements, ESI allows ports to encourage cleaner vessels through incentives. Ships performing beyond environmental regulations can receive recognition and financial benefits when calling at participating ports. 

This creates a market-based incentive structure that supports environmental improvements while maintaining operational flexibility for shipping companies. 

How the Environmental Ship Index Works

The Environmental Ship Index evaluates a ship’s environmental performance through a scoring system composed of several sub-scores.  

These reflect key emission categories including:  

• NOx emissions 

• SOx emissions 

• CO₂ performance 

• additional elements such as Onshore Power Supply (OPS) capability 

Together, these components form the overall ESI score, which ports use as a reference when applying environmental incentives. 

The Environmental Ship Index operates through a structured three-step process: 

1. Ships Register and Report Environmental Data

Ships participate in ESI by submitting relevant environmental data through the system. 

This typically includes: 

• Engine certification and NOx performance 

• Fuel use and SOx emissions 

• Distance sailed and bunker consumption (reported semi-annually) 

• Onshore Power Supply (OPS) capability 

• Bunker Delivery Notes (BDNs) 

The reporting scope is structured and limited, allowing participation without complex operational reporting requirements. 

2. Environmental Performance Is Converted into an ESI Score

OceanScore collects and verifies submitted environmental data and calculates the Environmental Ship Index score. 

The ESI Air Score is calculated using the formula: 

ESI Air Score = NOx + SOx + CO₂ + OPS 

The score reflects environmental performance beyond regulatory requirements and provides a consistent environmental benchmark used by ports. 

3. Ports Apply Incentives

Ports participating in the Environmental Ship Index define their own incentive schemes. 

Common incentives include: 

• Port fee discounts 

• Preferential treatment based on ESI score thresholds 

Once a vessel receives an ESI score, participating ports can automatically apply the relevant incentive when the ship calls. 

Even a single port call at an ESI participating port can already generate meaningful savings, often exceeding the administrative fee required to participate in the scheme. 

Environmental Ship Index Scores Explained

The Environmental Ship Index evaluates environmental performance across several dimensions. 

NOx Performance

The scheme evaluates nitrogen oxide emissions based on engine certification relative to IMO Tier standards.

Ships equipped with Tier II or Tier III engines typically achieve stronger NOx scores.

SOx Performance

Sulphur oxide scoring reflects fuel choice and emissions control technologies such as:

• ULSFO or VLSFO fuels

• Exhaust gas cleaning systems (scrubbers)

Ships operating with lower sulphur emissions receive higher SOx scores.

Greenhouse Gas Performance

The CO₂ component currently reflects the reporting of distance sailed and bunker consumed. Additional points can be granted where the relationship between fuel consumed and distance sailed improves over time. 

As the scheme continues to evolve, greenhouse gas performance may play a stronger role in overall scoring. 

Onshore Power Supply (OPS)

Ships equipped to connect to shore power can receive additional scoring benefits. 

In practice, a large share of the global fleet is already capable of achieving ESI scores that qualify for port fee incentives. Today, more than 70% of vessels can generate scores eligible for port fee reductions at participating ports. OceanScore supports shipping companies in identifying which vessels qualify and how participation can unlock these incentives. 

Who Can Register a Vessel in the Environmental Ship Index?

Participation in the Environmental Ship Index is flexible across the maritime value chain.

Vessel registration can be completed by:

• Ship owners

• Ship managers

• Charterers

• Vessel pools

• Shipping agents

This flexibility allows participation to be integrated into existing operational or technical management processes.

Benefits of ESI for Shipping Companies

Participation in the Environmental Ship Index offers both commercial and operational advantages. 

Port Fee Reductions

More than 100 leading ports across Asia, the Middle East, Australia, Europe, North America and South America offer incentives linked to ESI scores. 

For ships calling multiple participating ports, these incentives can accumulate into meaningful cost reductions. Even where vessel deployments cannot always be forecast in advance — as is often the case in segments such as dry bulk — the broad participation of ports makes the likelihood of capturing these incentives very high.

High Likelihood of Eligibility

A common misconception is that only the newest or most technically advanced vessels qualify for ESI incentives. 

In practice, every vessel can generate an ESI score. Even basic participation such as reporting distance sailed and bunker consumed generates an initial score, which already qualifies vessels for incentives in some ports. 

Many vessels achieve significantly higher scores when equipped with technologies or operational characteristics such as: 

• Tier II or Tier III engines 

• Use of VLSFO or ULSFO fuels 

• Exhaust gas cleaning systems (scrubbers) 

• Shore power capability 

In practice, many leading shipping companies register their entire fleets in ESI. The potential savings across multiple port calls typically outweigh the small administrative effort required for participation, making selective registration of only some vessels unnecessary. 

Low Participation Cost

Participation in the Environmental Ship Index involves only a modest administrative fee. 

In contrast to many other environmental schemes, ESI does not require additional inspections or verification processes, keeping the administrative burden low. 

In many cases, the savings generated from a single call at an ESI participating port already exceed this administrative fee. 

Benefits of ESI for Ports

Ports worldwide increasingly focus on improving environmental performance and air quality. The Environmental Ship Index provides a structured framework that allows ports to: 

• Incentivise cleaner vessels 

• Improve local air quality 

• Address Scope 3 emissions from vessel calls 

• Strengthen sustainability positioning 

Because scoring is calculated centrally by OceanScore, ports can implement incentive schemes without significant administrative burden. 

The Role of OceanScore

OceanScore is the globally mandated administrator of the Environmental Ship Index, supporting both shipping companies and ports. 

OceanScore’s responsibilities include: 

• Collecting and verifying environmental data 

• Calculating official ESI scores 

• Reporting scores back to participating ports in a consistent and transparent way, providing the data needed to apply environmental incentive schemes 

• Supporting participants with technical guidance 

• Maintaining transparency and integrity of the system 

Through its broader digital solutions, OceanScore also helps maritime stakeholders manage emissions data, regulatory exposure and environmental performance. 

Environmental Ship Index in the Context of Maritime Decarbonisation

As regulations such as EU ETS and FuelEU Maritime reshape the economics of shipping, environmental performance increasingly carries commercial implications. 

The Environmental Ship Index complements these developments by providing positive incentives rather than regulatory obligations. 

For shipping companies, this means environmental performance can translate into measurable financial benefits. For ports, the scheme supports cleaner air and sustainable port development. 

A Growing Global Network

Since its launch in 2011, the Environmental Ship Index has grown into the leading global port incentive scheme.

With more than 100 ports and over 6,800 vessels participating (as of March 2026), the network continues to expand as environmental performance becomes increasingly important across the maritime industry.

As adoption increases, the cumulative impact strengthens incentives for cleaner vessels and supports healthier port communities worldwide.

An Established Industry Benchmark

Since its introduction, the Environmental Ship Index has become the most widely adopted environmental incentive framework used by ports worldwide.

Studies analysing environmentally differentiated port infrastructure charges have shown that ESI provides a practical and transparent mechanism for rewarding ships that reduce emissions beyond regulatory requirements.

As adoption continues to grow, ESI helps align ports and ship operators around a common framework for recognising environmental performance.

Learn More About ESI Participation

If you want to explore participation in the Environmental Ship Index in more detail, see:

For shipping companies:

Environmental Ship Index for Shipping

For ports:

Environmental Ship Index for Ports

Frequently Asked Questions