MARPOL Annex VI has moved from being a regulation about smoke and sulphur to being one of the most commercially significant rule sets affecting your vessel. Since the carbon intensity measures came into force, every cargo ship of any size is now being measured, rated, and — increasingly — chosen or rejected by charterers partly on the basis of how efficiently it operates. This guide explains what Annex VI actually requires today, how the EEXI and CII work, what a D or E rating means, and how it all connects to vetting.
Two things sit at the centre of Annex VI compliance now: EEXI, a one-time measure of a ship's technical efficiency, and CII, an annual rating of how efficiently the ship is actually operated. The first is about design; the second is about how you run the vessel year after year.
What is MARPOL Annex VI?
MARPOL Annex VI is the chapter of the International Convention for the Prevention of Pollution from Ships that deals with air pollution. Historically it covered sulphur oxides (SOx), nitrogen oxides (NOx), particulate matter, ozone-depleting substances, and the use of compliant fuel. Compliance has always been evidenced by the International Air Pollution Prevention (IAPP) certificate, which Port State Control officers check as a matter of routine.
What has changed is the addition of the energy efficiency and carbon intensity framework. Annex VI now also governs how much carbon dioxide a ship emits relative to the work it does — and this is where the EEXI, the CII, and the SEEMP come in. For most owners today, "Annex VI compliance" increasingly means the carbon intensity rules, because those are the ones that are tightening every year and feeding into commercial decisions.
EEXI — the One-Time Technical Requirement
The Energy Efficiency Existing Ship Index (EEXI) applies the design-efficiency logic of new-build ships to the existing fleet. Existing ships of 400 gross tonnage and above, of the types covered by the EEDI framework, must calculate their attained EEXI and demonstrate that it meets a required value based on a reduction factor against a baseline.
EEXI is essentially a one-time exercise. It is a technical characteristic of the ship — if the attained value does not meet the required value, owners typically address it through measures such as engine power limitation (EPL), shaft power limitation, or other efficiency modifications, and then it is verified and certified. Once compliant, the EEXI does not need to be recalculated every year the way the CII does.
Think of EEXI as a one-off entry ticket and CII as the ongoing performance review. A ship can be fully EEXI-compliant and still earn a poor CII rating, because EEXI measures design potential while CII measures real operational behaviour.
CII — the Annual Operational Rating
The Carbon Intensity Indicator (CII) is the one that demands ongoing attention. It applies to cargo, RoPax and cruise ships of 5,000 gross tonnage and above — the same ships that already report fuel oil consumption under the IMO Data Collection System (DCS). Each year, the ship's actual carbon intensity is calculated from its fuel consumption and the distance it travelled, and the ship is given a rating from A to E.
Because the calculation is based on real operational data, the CII reflects how the ship was actually run: its speed, its laden-versus-ballast profile, time spent at anchor, hull and machinery condition, and voyage efficiency all feed into it. Two identical sister ships can earn very different CII ratings depending purely on how they are operated.
The A-to-E rating scale
C is the line a ship needs to stay at or above. A and B are superior; D and E indicate inferior performance that the regulation expects you to correct.
The required carbon intensity tightens every year through a reduction factor against a 2019 baseline. This means a ship that changes nothing about how it operates will tend to drift downward through the rating bands over time — yesterday's C can become tomorrow's D without the ship doing anything differently. Standing still is, in effect, going backwards.
SEEMP Part III and Corrective Action Plans
The Ship Energy Efficiency Management Plan (SEEMP) is the document that ties the CII framework together on board. Its third part — SEEMP Part III — is the carbon intensity improvement plan, setting out the ship's required ratings for coming years and the measures planned to achieve them. It is subject to verification and is checked during inspections.
The consequence built into the regulation is specific. A ship that is rated D for three consecutive years, or E for a single year, must develop a corrective action plan within its SEEMP Part III, showing how it will achieve a C rating or above. This is not optional paperwork — it is a defined regulatory trigger with a defined response.
What Annex VI Carbon Intensity Compliance Requires on Board
- Valid International Air Pollution Prevention (IAPP) certificate
- Attained EEXI calculated, verified, and meeting the required value
- Annual fuel oil consumption data reported under the IMO DCS
- Annual CII calculated and the A–E rating recorded
- SEEMP Part III in place, verified, and reflecting the ship's required ratings
- Corrective action plan prepared if rated D for three years or E for one year
How Annex VI Connects to PSC and Vetting
Annex VI is not just an environmental box-ticking exercise — it shows up in both regulatory and commercial inspections. Port State Control officers verify the IAPP certificate and the supporting documentation, and deficiencies in this area are recorded like any other. But the larger consequence is commercial.
RightShip and other vetting frameworks now factor environmental performance into their assessments. A poor CII rating sits alongside your safety record in the way charterers see your vessel. As we cover in our guide to the RightShip rating, a D or E carbon intensity rating increasingly draws additional scrutiny from environmentally focused charterers — even for a vessel with an otherwise strong safety profile. In a tightening market, two vessels with equal safety records can be separated on their environmental rating alone.
This is the key shift for owners to understand: carbon intensity is no longer only a compliance question for the technical department. It is becoming a commercial differentiator that the chartering desk has to care about — the same way a PSC detention or a weak RISQ inspection result does.
Practical Steps to Protect Your Rating
Carbon intensity is not something you can fix in the week before a survey — it is the product of a full year of operation. The owners who manage it well treat it as an ongoing operational discipline rather than an annual reporting task:
- Monitor CII continuously through the year, not just at year-end — if you only find out the rating after the fact, it is already too late to influence it.
- Optimise speed and voyage planning — speed has a disproportionate effect on fuel consumption and is often the largest single lever available.
- Manage hull and propeller condition — fouling increases resistance and fuel burn directly; timely cleaning and coatings pay back in CII terms.
- Reduce time at anchor and optimise port turnarounds where commercially possible, since idle and inefficient time still counts against the ship.
- Keep SEEMP Part III live and realistic — use it as a working plan, not a document filed and forgotten until the next inspection.
- Engage the chartering and operations teams, not just the technical department — many of the levers that move CII sit with how the ship is employed and operated.
The regulatory landscape here is still developing — the IMO continues to review the effectiveness of these measures and to work on the next phase of the framework. But the direction is settled: carbon intensity requirements get stricter over time, and the commercial weight attached to them grows. Owners who build the monitoring and the operational habits now will be far better placed than those who wait to react to a poor rating.
Frequently Asked Questions
EEXI is a one-time technical index that measures a ship's design energy efficiency — it is calculated once and the ship must meet the required value. CII is an annual operational rating that measures how efficiently the ship is actually operated each year, expressed as a grade from A to E based on real fuel consumption and distance travelled.
The CII rating applies to cargo, RoPax and cruise ships of 5,000 gross tonnage and above — the same ships that already report fuel oil consumption data under the IMO Data Collection System (DCS). EEXI applies more broadly to existing ships of 400 gross tonnage and above of the types covered by the EEDI framework.
A ship rated D for three consecutive years, or E for a single year, must develop a corrective action plan within its SEEMP Part III setting out how it will reach a C rating or above. Beyond the regulation itself, a poor CII rating increasingly affects commercial employability, as charterers and platforms such as RightShip factor environmental performance into their vetting decisions.
Each ship has a required carbon intensity that is tightened year on year by a reduction factor relative to a 2019 baseline. Because the boundaries get stricter every year, a ship that does nothing to improve its efficiency will tend to slide down the A-to-E scale over time even if its actual emissions stay the same.