Vessel API's /emissions endpoint provides *verifiable* ship CO2 estimates

This review examines Vessel API's /emissions endpoint, which calculates ship CO2 emissions by addressing complex factors like fuel type, EEXI, and the absence of direct consumption data.

TL;DR

Best for: Companies, carbon accountants, and regulators needing verifiable, per-voyage ship CO₂ emissions data without direct access to a vessel's fuel logs. Skip if: You have direct, real-time access to a ship's fuel consumption data, or if rough, non-auditable estimates are sufficient for your use case. Bottom line: Vessel API offers a technically sound, API-driven solution for estimating complex ship CO₂ emissions from publicly available vessel characteristics and voyage data, designed for regulatory compliance.

METHODOLOGY

This v0 review draws on the founder's published claims regarding the Vessel API's /emissions endpoint, as detailed in the blog post "How to Measure a Ship's CO₂ Emissions From Land." The review covers the technical claims and utility of this niche API based on the provided explanation of its underlying methodology. Independent benchmarks are pending. We will re-test when claims diverge from observed behavior.

• Tool: Vessel API's /emissions endpoint (version not specified)
• Date Observed: 2026-05-20
• Source Signal URL: https://dev.to/vessel_api/how-to-measure-a-ships-co2-emissions-from-land-2c2
• What's Covered: The review covers the founder's claims regarding the methodology for estimating ship CO₂ emissions, including the role of specific carbon factors for different fuel types (HFO, VLSFO, MGO, LNG) and the application of the Energy Efficiency Existing Ship Index (EEXI). It details how the API addresses the challenge of lacking direct fuel consumption data.
• What's NOT Covered: This v0 review does not include independent performance benchmarks, long-term workflow integration analysis, or an exhaustive examination of edge cases beyond those discussed in the source article. Specific API input/output schemas, latency, and rate limits are also not covered.

WHAT IT DOES

The Vessel API's /emissions endpoint aims to provide a verifiable estimate of a ship's CO₂ output for a given voyage, even when direct fuel consumption data is unavailable. It addresses the complexities of marine emissions by integrating multiple data points and regulatory frameworks.

Estimating fuel consumption

The core challenge in calculating ship emissions from land is the lack of public, per-voyage fuel consumption data. While aggregate annual data is reported under the IMO Data Collection System and per-voyage data for European ports is collected by the EU MRV regime, neither is publicly accessible. The API works around this by estimating fuel consumption. This estimation process involves working backward from a ship's design specifications and adjusting for probable actual usage, a critical step for external parties seeking accurate figures.

Precise carbon factors

The API incorporates specific, non-interchangeable carbon factors published by the IMO for various marine fuel types. These factors are crucial for regulatory compliance. For instance, heavy fuel oil (HFO) has a factor of 3.114 grams of CO₂ per gram of fuel burned, VLSFO (very low sulfur fuel oil) is 3.151, marine gas oil (MGO) is 3.206, and LNG's direct combustion factor is 2.750. Using the wrong factor, even if the numbers appear close, will lead to verification failure in regulatory reports.

EEXI as a baseline

To establish a baseline for a vessel's fuel economy, the API leverages the Energy Efficiency Existing Ship Index (EEXI). EEXI serves as a fuel economy rating, similar to an MPG sticker for cars, but for ships of 5,000 gross tonnes and above. This index, typically found in classification society databases, provides a standardized measure of a ship's design efficiency, which the API uses to inform its fuel consumption estimates.

WHAT'S INTERESTING / WHAT'S NOT

What's interesting about Vessel API's approach is its explicit acknowledgment and systematic handling of the data gaps inherent in measuring ship emissions from land. The founder's detailed explanation of why direct fuel consumption data is unavailable and how the API works around this limitation provides significant value. The emphasis on regulatory compliance, specifically referencing IMO Data Collection System and EU MRV, positions the tool as a serious contender for use cases requiring auditable numbers. The precise enumeration of carbon factors for HFO, VLSFO, MGO, and LNG, coupled with the warning about their non-interchangeability, highlights a deep understanding of the domain. Furthermore, the use of EEXI as a public, standardized proxy for vessel efficiency is a pragmatic solution to a complex problem, offering a transparent basis for estimation.

What's less interesting, or rather, what's missing from this particular signal, is a more concrete demonstration of the API itself. The blog post focuses heavily on the underlying methodology and the why behind the calculations, but offers limited insight into the what of the API's interface. There are no specific examples of API calls, input parameters, or output structures. While the methodological transparency is commendable, the absence of practical API usage examples makes it harder to immediately assess integration complexity or the richness of the data returned. The article also does not delve into the specific algorithms or models used to adjust EEXI baselines for actual voyage conditions, such as propeller polishing or hull fouling, which are mentioned as relevant factors.

PRICING

Pricing information for the Vessel API's /emissions endpoint was not provided in the source material. (Pricing snapshot date: 2026-05-20)

VERDICT

Vessel API's /emissions endpoint is a strong solution for organizations that need to calculate verifiable ship CO₂ emissions without direct access to a vessel's fuel logs. Its strength lies in its methodical approach to estimating fuel consumption, leveraging precise IMO carbon factors and the EEXI as a robust baseline. This makes it particularly suitable for carbon accounting, regulatory reporting (like EU MRV), and supply chain transparency initiatives where accuracy and auditability are paramount. If your use case involves tracking emissions for a fleet you do not directly operate, or for historical voyages where fuel data is inaccessible, this API provides a technically sound and transparent path to obtaining credible CO₂ estimates.

WHAT WE'D TEST NEXT

Our next steps would involve a hands-on evaluation of the /emissions endpoint. We would test the API's input parameters and output schema to understand data granularity and format. Benchmarking latency and throughput would be critical for assessing its suitability for high-volume applications. We would also investigate the API's coverage across different vessel types, sizes, and geographical routes. A key area for future testing would be to compare the API's estimated emissions against known (though non-public) EU MRV or IMO DCS data for a sample set of voyages to validate its accuracy and the robustness of its estimation models. Finally, we would explore the API's ability to account for real-world operational variables like speed changes, weather conditions, and hull maintenance status.