Carbon intensity compliance of a crude oil tanker: A five-year voyage-level analysis

Öz

The Carbon Intensity Indicator (CII) of ships is evaluated annually; however, this aggregated calculation may conceal substantial variation in carbon intensity across different voyage types. To investigate how voyage parameters affect CII outcomes, this study presents a five-year (2020–2024) voyage-level empirical analysis of a Suezmax crude oil tanker. The findings indicate that laden voyages with high waiting time (>40% of voyage days) exhibit the poorest CII performance, averaging 4.84 gCO₂/dwt·nm, well above the 2024 required threshold of 3.30 gCO₂/dwt · nm. Speed reduction in both laden and ballast conditions produces meaningful but bounded fuel savings well below cubic-law expectations, and the vessel's rating trajectory was shaped less by operational change than by the tightening of the regulatory threshold itself. The findings underline the importance of voyage-level analysis as a complement to annual reporting and indicate that ship operators should consider voyage characteristics and idle time alongside speed optimization, particularly as reduction factors continue to escalate.

Anahtar Kelimeler

• Carbon intensity indicator
• Operational efficiency
• Tanker operations
• Fuel consumption

Teşekkür

The authors acknowledge the vessel operator for providing access to the operational data used in this study.

Kaynakça

1. [1] IMO. Fourth IMO GHG Study 2020. 2020. [Online] Available from: https://www.imo.org/en/OurWork/Environment/Pages/Fourth-IMO-Greenhouse-Gas-Study-2020.aspx (Accessed: 15/01/2026).
2. [2] IMO. 2023 IMO Strategy on Reduction of GHG Emissions from Ships, Resolution MEPC.377(80). 2023. [Online] Available from: https://www.imo.org/en/OurWork/Environment/Pages/2023-IMO-Strategy-on-Reduction-of-GHG-Emissions-from-Ships.aspx (Accessed: 15/01/2026).
3. [3] IMO. 2022 Guidelines on Operational Carbon Intensity Indicators and the Calculation Methods (CII Guidelines, G1), Resolution MEPC.352(78). 2022. [Online] Available from: https://wwwcdn.imo.org/localresources/en/OurWork/Environment/Documents/Air%20pollution/MEPC.352(78).pdf (Accessed: 15/01/2026).
4. [4] Sönmez Hİ. The impact of IMO Regulations on ship emission research: A bibliometric analysis. Seatific Journal 2025; 5(2): 79–90.
5. [5] IMO. 2022 Guidelines on Operational Carbon Intensity Rating of Ships, Resolution MEPC.354(78). 2022. [Online] Available from: https://wwwcdn.imo.org/localresources/en/OurWork/Environment/Documents/Air%20pollution/MEPC.354(78).pdf (Accessed: 15/01/2026).
6. [6] IMO. 2021 Guidelines on Operational Carbon Intensity Reduction Factors Relative to Reference Lines, Resolution MEPC.338(76). 2021. [Online] Available from: https://wwwcdn.imo.org/localresources/en/OurWork/Environment/Documents/Air%20pollution/MEPC.338(76).pdf (Accessed: 15/01/2026).
7. [7] Sardar A, Anantharaman M, Islam TMR, Garaniya V. Data collection framework for enhanced carbon intensity indicator (CII) in the oil tankers. The Canadian Journal of Chemical Engineering 2025; 103(1): 170-187.
8. [8] Wang S, Psaraftis HN, Qi J. Paradox of International Maritime Organization's carbon intensity indicator. Communications in Transportation Research 2021; 1: 100005.

9. [9] Yuan Q, Wang S, Peng J. Operational efficiency optimization method for ship fleet to comply with the carbon intensity indicator (CII) regulation. Ocean Engineering 2023; 286: 115487.
10. [10] Adland R, Cariou P, Wolff F-C. Optimal ship speed and the cubic law revisited: Empirical evidence from an oil tanker fleet. Transportation Research Part E 2020; 140: 101972.
11. [11] IMO. 2024 Guidelines for the Development of a Ship Energy Efficiency Management Plan (SEEMP), Resolution MEPC.395(82). 2024. [Online] Available from: https://wwwcdn.imo.org/localresources/en/OurWork/Environment/Documents/Air%20pollution/MEPC.395(82).pdf (Accessed: 15/01/2026).
12. [12] IMO. 2022 Interim Guidelines on Correction Factors and Voyage Adjustments for CII Calculations (CII Guidelines, G5), Resolution MEPC.355(78). 2022. [Online] Available from: https://wwwcdn.imo.org/localresources/en/OurWork/Environment/Documents/Air%20pollution/MEPC.355(78).pdf (Accessed: 15/01/2026).
13. [13] Carlton J. Marine Propellers and Propulsion. 3rd ed. Butterworth-Heinemann, Oxford, UK, 2012.
14. [14] Psaraftis HN, Kontovas CA. Speed models for energy-efficient maritime transportation: A taxonomy and survey. Transportation Research Part C 2013; 26: 331-351.
15. [15] Masodzadeh PG, Ölçer AI, Ballini F, Christodoulou A. Live carbon-tracking mechanism for ships, a methodology to mitigate uncertainties in the carbon intensity calculations. Transportation Research Interdisciplinary Perspectives 2024; 23: 101004.
16. [16] Lindstad E, Asbjørnslett BE, Strømman AH. The importance of economies of scale for reductions in greenhouse gas emissions from shipping. Energy Policy 2012; 46: 386-398.
17. [17] Lindstad E, Eskeland GS. Low carbon maritime transport: How speed, size and slenderness amounts to substantial capital energy substitution. Transportation Research Part D 2015; 41: 244-256.
18. [18] Cariou P. Is slow steaming a sustainable means of reducing CO₂ emissions from container shipping? Transportation Research Part D 2011; 16(3): 260-264.
19. [19] Elkafas AG, Rivarolo M, Massardo AF. Environmental economic analysis of speed reduction measure onboard container ships. Environmental Science and Pollution Research 2023; 30: 59645-59659.
20. [20] Hua R, Yin J, Wang S, Han Y, Wang X. Speed optimization for maximizing the ship's economic benefits considering the Carbon Intensity Indicator (CII). Ocean Engineering 2024; 293: 116712.
21. [21] Elkafas AG, Shouman MR. Assessment of energy efficiency and ship emissions from speed reduction measures on a medium sized container ship. Transactions of the Royal Institution of Naval Architects Part A: International Journal of Maritime Engineering 2021; 163: 121-132.
22. [22] Yan D, Chen C, Gan W, Sasa K, He G, Yu H. Carbon intensity indicator (CII) compliance: Applications of ship speed optimization on each leg in a voyage. Ocean Engineering 2023; 285: 115461.
23. [23] Yang L, Chen G, Zhao J, Rytter NGM. Ship speed optimization considering ocean currents to enhance environmental sustainability in maritime shipping. Sustainability 2020; 12(9): 3649.
24. [24] Rauca L, Batrinca G. Impact of Carbon Intensity Indicator on the vessels' operation and analysis of onboard operational measures. Sustainability 2023; 15(14): 11387.
25. [25] Sun L, Wang X, Lu Y, Hu Z. Assessment of ship speed, operational carbon intensity indicator penalty and charterer profit of time charter ships. Heliyon 2023; 9(10): e20719.
26. [26] Lagouvardou S. A critical review of bunker adjustment factors and their impact on shipping decarbonization. Maritime Economics & Logistics 2022; 24: 737-756.
27. [27] Chen R. Analysis for decarbonization pathways for shipping. E3S Web of Conferences 2023; 424: 03007.
28. [28] Seyhan A, Sevgili C, Bayraktar M, Yüksel O. Benchmarking reference bulk carriers with the best international shipping results regarding carbon intensity indices. Seatific Journal 2025; 5(2): 70–78.