Sustainable drop-in fuels: driving down vehicle emissions today

High costs, charging concerns and operational challenges can make zero-emission commercial vehicles impractical and unaffordable in the short term. In the meantime, sustainable drop-in fuels, such as hydrotreated vegetable oil and biomethane, could be the answer. Jackie Savage, programme manager at Zemo Partnership, explores how fleets can ensure the environmental credentials of such fuels

As UK businesses face intensifying pressure to meet corporate sustainability goals and regulatory demands, the decarbonisation of commercial fleets, especially HGVs, has become a strategic priority. Yet the dominance of battery-electric vehicles in public discourse often overlooks a critical reality: for many fleet operators, practical, financial, and operational constraints make the transition to zero tailpipe emission vehicles a long-term prospect rather than a short-term solution.

Zemo Partnership’s Renewable Fuels Assurance Scheme (RFAS) and the newly launched ‘RFAS Fleet’ provide a credible, scalable pathway to emissions reduction, available today, by unlocking the full potential of sustainable low-carbon fuels.

The barriers to electrification

The electrification of HGV fleets can present considerable barriers: high upfront vehicle costs, limited availability of electric models, depot infrastructure upgrades, and reliance on grid capacity upgrades that can take years to implement. For many operators, especially those running time-critical logistics or off-road operations, these challenges render the electric transition either impractical or unaffordable in the short term.

In contrast, sustainable drop-in fuels such as hydrotreated vegetable oil (HVO) and biomethane offer an immediate, lower-cost solution. These fuels are compatible with existing vehicle technologies and refuelling infrastructure, allowing fleets to dramatically reduce greenhouse gas (GHG) emissions without disrupting day-to-day operations.

Lifecycle emissions savings from renewable fuels can exceed 80 per cent compared to fossil diesel and gas. In some cases, such as biomethane derived from manure, GHG emissions savings can surpass 100 per cent due to the capture of fugitive methane that would otherwise enter the atmosphere. 

The UK is seeing growing supplies of renewable diesel and biomethane, as well as increased availability of sustainable biodiesel. Zemo’s monitoring of the low carbon fuels market reveals that well over 800 organisations are deploying RFAS approved sustainable fuels in their fleets.

Genuine climate benefits

Fleet operators are increasingly seeking assurance that renewable fuels deliver genuine climate benefits and do not create unintended harm to land or biodiversity.     
This is where RFAS plays a crucial role.

Managed by Zemo Partnership, RFAS is the UK’s leading independent sustainability assurance scheme for verifying the environmental integrity of low-carbon fuels used in commercial vehicles. It certifies that the fuel: is derived from sustainably sourced  feedstocks; achieves verified GHG emissions savings, and is fully traceable through the supply chain.

Under RFAS, fuel transactions are supported by a Renewable Fuel Declaration, providing supply chain specific GHG emissions data for the volume of fuel purchased. These declarations are customer specific and non-transferable, ensuring clear chain-of-custody and preventing greenwashing.

All suppliers in the fuel chain must be RFAS-approved, and are subject to ongoing compliance monitoring involving annual audits. This process gives fleet operators confidence in the sustainability of the fuels purchased from any of RFAS’s 54 approved companies supplying biodiesel, renewable diesel (including HVO) and biomethane. 

End customers

While RFAS assures the sustainability of fuels purchased by fleet operators, the new RFAS Fleet scheme extends that assurance downstream to end customers; companies that procure logistics or construction services and are accountable for Scope 3 emissions (those from their supply chains). Through Fleet GHG Emissions Declarations, fleet operators provide their customers with independently verified, journey specific environmental information detailing the type and volume of renewable fuel used; renewable fuel feedstock provenance, and verified well-to-wheel GHG emissions savings.

For businesses focused on ESG reporting and carbon accounting, this represents a trusted mechanism to quantify and report on transport-related Scope 3 emissions, something that has historically been challenging due to data fragmentation and lack of verification.

For fleet operators, RFAS Fleet provides a powerful competitive edge in a market where sustainability credentials are increasingly influencing procurement decisions. By evidencing the use of renewable fuels, operators can enhance their appeal in contract tenders, meet client requirements, and differentiate themselves in a cost-sensitive and environmentally conscious market.

One of RFAS Fleet’s key innovations is the ability to use a ‘virtual’ allocation model, which supports operators working across distributed networks where direct access to renewable fuels may be limited or practically unviable. In practice, this means that while a specific vehicle may run on conventional fuel, another vehicle within the same fleet consumes an equivalent volume of RFAS-approved renewable fuel. The mass balance methodology prevents double counting of fuel volumes or GHG emissions savings, and goes beyond ‘book and claim’ schemes to deliver full traceability, by linking the sustainability credentials with physical transactions. 

This approach helps support higher utilisation of sustainable fuels across the network, whilst offering customers credible and verifiable proof of sustainability. 
Zemo Partnership designed RFAS Fleet to be straightforward to implement, working closely with leading logistics firms like Gregory Distribution (the first RFAS Fleet-approved operator) and Howard Tenens to ensure the process aligns with existing fuel management systems and business workflows.     

To join the scheme, operators must complete the RFAS Fleet application form and undergo a successful application audit to verify compliance with the scheme’s Performance Standards. They must also receive an RFAS Fleet Approval Document and be listed on the RFAS Fleet website.

Approved operators are subject to annual audits to maintain their status. Zemo-appointed auditors verify both the accuracy of fuel allocations and the disclosure of GHG emissions data associated with the journeys undertaken on behalf of the customer.

Low risk, high impact

In the push toward net zero, RFAS and RFAS Fleet offer a low-risk, high-impact solution for fleet decarbonisation. For HGV fleets, the schemes help address both: Scope 1 emissions (from owned vehicles and machinery) and Scope 3 emissions (from outsourced transport and logistics services). The use of RFAS-approved fuels allows operators to decarbonise today, with confidence in the quality, sustainability, and emissions performance of their fuel.

While the focus is currently on high blend biodiesel, HVO, and biomethane, RFAS has already expanded to support renewable hydrogen suppliers and users. 
Looking ahead, Zemo Partnership plan to expand RFAS Fleet to encompass renewable electricity used in electric vehicles, ensuring the scheme keeps pace with future technologies and continues to offer robust verification across a broader spectrum of low-carbon solutions.

Fleet decarbonisation isn’t just a long-term goal, it’s a present-day imperative. Zemo Partnership’s RFAS and RFAS Fleet provide commercial vehicle operators with the tools to take meaningful action now, cutting emissions, enhancing credibility, and winning new business. In an industry where reliability, cost control, and customer expectations are paramount, these schemes offer a pragmatic route to sustainability, helping fleets reduce their climate impact without compromising operational performance. 

Further information, including the Technical Guidance for each scheme and a list of approved companies, can be found on the RFAS and RFAS Fleet webpages, or by contacting Zemo Partnership at rfs@zemo.org.uk.