Understanding certification, carbon metrics, and quality control in marine biofuels

Marine biofuels offer real carbon reduction potential, but harnessing them requires a firm understanding of certification, documentation, specification, and regulatory nuance — and partnering with a supplier who knows how to navigate it all. 

There's no shortage of interest in marine biofuels, but there is still plenty of confusion about how to use them credibly and compliantly. FuelEU Maritime, IMO CII, regional emissions trading schemes, and increasing pressure from charterers on Scope 3 emissions have moved biofuels into a compliance-critical category. But for all the industry's enthusiasm, confusion still surrounds how biofuels are certified, what quality parameters actually mean, and how carbon savings are counted and claimed. 

In this article, I will be looking at these factors in more detail and asking: how can shipowners and operators ensure that the marine biofuels they procure genuinely deliver certified, reportable carbon reductions and not just a blend label?

From POS to POC: The new language of compliance 

One of the first hurdles a biofuel buyer must negotiate is understanding the difference between a POS and a POC. Here's a quick summary: 

POS (Proof of Sustainability) could be thought of as the "birth certificate" of a biofuel. A POS is an official document that proves a fuel has met specific sustainability standards. These commonly include where the feedstock (e.g., used cooking oil, animal fat) came from, how it was processed, and what the total greenhouse gas (GHG) emissions savings are compared to fossil fuels. 

A POS will be issued under certification schemes like ISCC or RSB, and it's designed to give fuel buyers clear, verifiable evidence that the fuel they purchased is environmentally compliant and traceable all the way back to its origin. 

In most cases, this POS travels with the fuel all the way to the shipowner, who can then use it for emissions reporting (e.g., under EU MRV or IMO DCS). 

POC (Proof of Compliance) is a substitute certificate when the POS can't be passed on. Sometimes, the POS has to be "retired", usually because the supplier has used it to claim a regulatory incentive, such as a subsidy or tax credit. 

In these cases, the actual POS can't be handed over to the shipowner because, in effect, it's been used already. Instead, the shipowner receives a POC: a Proof of Compliance. 

A POC confirms that the fuel delivered was compliant, certified, and eligible for GHG reduction claims. It serves the same purpose for reporting, just without the original POS document attached. 

A common misconception is that these documents accompany the bunker delivery note (BDN) at the point of supply. In practice, both POS and POC documents are typically issued 30 to 45 days post-delivery, due to the time required to balance and verify system inputs through the certified chain of custody. 

Critically, both POS and POC are valid for EU MRV, IMO DCS, and emerging GHG compliance frameworks. What matters is understanding what you've received and how to use it.

Mass balance: Why a B30 blend isn't always 30% biofuel 

Let's tackle one of the most misunderstood concepts in marine biofuels: mass balance. 

ISCC EU is the dominant sustainability certification scheme for marine fuels. Under this scheme, the mass balance system allows sustainable and non-sustainable fuels to be co-processed, stored, and distributed in shared infrastructure, provided that the total inputs and outputs are tracked and reconciled across the system. This enables suppliers to certify GHG reductions even when the physical product delivered isn't homogeneously blended. 

In practice, a customer requesting a B30 blend (30% biofuel) may physically receive a B15 or B20 — and still be entitled to claim 30% GHG reduction. This is because the remaining bio-component has been delivered to another vessel within the same audited supply chain. Over the accounting period, the system remains balanced. 

This principle is critical in real-world port and terminal operations, where segregating every product type would be logistically prohibitive and economically unworkable. Mass balance enables the scalability of sustainable fuels without compromising certification. 

ISCC-certified suppliers must undergo annual audits, implement chain-of-custody traceability, and manage detailed documentation to ensure compliance. RSB (Roundtable on Sustainable Biomaterials) is an alternative scheme, but ISCC remains the most widely recognized and adopted for maritime use, particularly under RED II/III regulations in Europe. 

Carbon has no borders. Whether your vessel burns the exact molecular blend or not, certified carbon reduction is valid, reportable, and verifiable.

Not all FAME is the same: Understanding specifications 

Another point of confusion is the specification for the bio-component and the delivered blend. 

Every biofuel originates from a feedstock and is refined into a final product, typically a Fatty Acid Methyl Ester (FAME) or Hydrotreated Vegetable Oil (HVO). The bio-component itself is subject to one of several international standards, such as: 

• EN 14214 – European standard for FAME used in diesel engines
• ASTM D6751 – US standard for biodiesel quality
• EN 15940 – European standard for paraffinic diesel fuels (e.g., HVO)
• ASTM D975 – US standard for road diesel (US HVO or RD99) 

When this bio-component is blended into marine fuel, the delivered product should then also meet ISO 8217 marine specifications — preferably ISO 8217:2024 RF or DF grades; however, ISO 8217:2017 with exceptions remains common in the market.  ISO standards ensure compatibility with marine engines, fuel systems, and operational performance. 

Importantly, some suppliers may offer FAME bottoms or FAME residue from biodiesel production at a lower cost, typically $40–$60 per tonne cheaper. Also known as "unregulated FAME", these fuels may not meet any recognized bio-specification such as EN 14214 and may carry higher risks of instability or contamination — even if the final blended product is guaranteed to meet ISO specifications. ISO 8217:2024 requires FAME to meet either EN14214 or ASTM D6751 prior to blending; as such, most, if not all, blends using FAME bottoms would need to be guaranteed under 2017, with exceptions.  

For full oversight of a bunker fuel being stemmed, always ask for a Certificate of Quality (COQ) for both the bio component and the fossil portion prior to blending, as well as the COQ of the blended product.

GHG targets: FuelEU vs. IMO — one emission, two rulers 

While marine fuels have a single emissions outcome, they are now measured against multiple regulatory baselines. This has major implications for how GHG reductions are calculated and how fuel buyers assess their options. For example, the following disparate baseline emissions factors may soon apply to biofuel: 

• ​​FuelEU Maritime uses a baseline of 91.16 gCO₂e/MJ​
• ​​The IMO's proposed GHG Fuel Standard (GFS) uses 93.34 gCO₂e/MJ​ 

Therefore, a biofuel claiming an "80% reduction" must emit no more than: 

• ​​18.24 gCO₂e/MJ under FuelEU​
• ​​18.66 gCO₂e/MJ under IMO​ 

This seemingly minor variation can materially affect fuel selection and compliance, and consumers should remain vigilant for regulatory overlaps between FuelEU, IMO CII, ETS, etc. 

Bridging the knowledge gap 

Perhaps the most underappreciated risk in marine biofuels today is the asymmetry of knowledge, not just among buyers, but also among suppliers and even regulators. 

The complexity of the compliance regime for certified biofuel deliveries has been challenging for early adopters. Roughly half of customers requesting biofuels still encounter difficulty distinguishing between POS and POC, or how to specify their carbon intensity preferences, and hurdles remain around feedstock provenance, delivery timing, documentation standards, and mass balance variability. 

To support customers, World Fuel has developed internal templates to standardize customer inquiries and supplier quotes, ensuring all parties capture these critical details from the outset. We also invest in training our global teams to help buyers pursue compliance effectively and ensure our own supply chain is equally informed, consistent, and transparent. 

Conclusion: Confidence over complexity 

Marine biofuels are maturing from 'alternative' fuels into active, available, and increasingly essential fuels for decarbonization. But success depends on more than supply. The true differentiators are certification credibility, specification clarity, and reporting readiness.