Introduction: geologically balanced fuels and the need for high-integrity certification

Geologically Balanced Fuels (GBFs) represent a novel approach to aligning fossil aviation fuel use with net-zero objectives as a complementary strategy to sustainable aviation fuels. By pairing conventional kerosene with geologically stored CO2 units that match its life-cycle emissions, GBFs operationalise a ‘like-for-like’ offsetting principle. This method is consistent with the goal of ‘geological net zero’, requiring long-lived CO2 emissions to be counterbalanced with equally durable carbon removals. A GBF comprises two distinct components: the physical fuel delivery following the conventional supply chain, and climate attributes in the form of geological storage or removal units, which are unbundled but sold jointly by the fuel supplier.

Are existing certification frameworks GBF-ready?

Currently, no single existing policy or certification framework can be adopted ‘as-is’ to certify geological CO2 offsets for aviation. While the Paris Agreement Article 6.4 offers a high-integrity ceiling, the supply of these credits remains uncertain. The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) Lower Carbon Aviation Fuels (LCAFs) framework provides the closest fit and serves as a strong foundation for GBF certification, provided targeted amendments are made. To incentivise this approach, GBFs would need recognition as an additional fuel category within existing policies, necessitating revised accounting and certification rules that combine life-cycle emission quantification with storage verification.

Amending LCAFs for GBF inclusion

LCAFs are traditional jet fuels with reduced carbon intensity due to mitigation measures like Carbon Capture and Storage (CCS) during production. Two fundamental amendments are required for the LCAF framework to support GBF certification. First, boundary expansion is necessary to count CCS activities that are operationally independent from or merely co-located with fuel production. Second, the emissions reduction threshold must evolve; currently, LCAFs only require a minimum 10% reduction. Full GBF alignment would require progressively increasing this threshold to 100% emissions reductions to enable net-zero aligned, like-for-like balancing of fossil kerosene emissions.

Counterfactuals and additionality

LCAF baselines are currently anchored to a global fossil fuel carbon intensity (CI) ceiling of 89 gCO2e/MJ. This global nature means that regions with naturally low fossil fuel CI require minimal intervention to meet eligibility. GBF alignment requires regional baselines that reflect the diverse CI of fossil fuel production. Furthermore, additionality tests must be differentiated by pathway. For Direct Air Capture with CCS (DACCS), a zero-emissions baseline may be acceptable due to high capital costs and absent demand signals. Conversely, for point-source CCS, benchmarks should reflect counterfactual deployment of captured CO2 streams and apply ambitious performance-based standards anchored to the best available technology.

Quantification, system boundaries and life-cycle assessment

Quantification rules must accurately capture the full life-cycle emissions of fuel production alongside CO2 removals. To align with GBFs, the 10% CI threshold must be replaced by a net greenhouse gas (GHG) reduction requirement scalable to 100%. The report recommends separate quantification and reporting of emission reductions versus carbon removals to prevent mitigation deterrence. For Bioenergy with CCS (BECCS), the report suggests matching the rigorous CORSIA SAF standard for biomass leakage treatment, including consequential assessments of indirect land-use change, rather than using weaker methodologies like those found in the EU Carbon Removal Certification Framework (CRCF).

Monitoring, reporting and verification (MRV), and permanence

MRV requirements must ensure that geological storage is maintained on timescales commensurate with the atmospheric lifetime of fossil CO2, effectively spanning millennia. Verification must be explicitly ex-post, focusing on actual outcomes rather than projected performance. On permanence, operators must remain responsible for monitoring and site sealing after closure for a sufficient period to ensure minimal release risk. Following this, liability should transfer to competent authorities, consistent with EU CCS Directive logic. Operators and fuel producers should also be held liable for replenishing reserve accounts in the event of avoidable reversals.

Accounting integrity

Accounting rules must prevent double-claiming, where the same geological CO2 storage unit is credited under multiple schemes, such as both an EU ETS compliance unit and a GBF attribute under CORSIA. Fuel reporting entities should be required to demonstrate the retirement of GBF credits equal to their compliance obligations, modelled on California’s Low Carbon Fuel Standard (LCFS) mechanics. This requires the development of interoperable registry linkages between GBF registries and other relevant compliance registries, such as national inventories and the EU ETS.

Sustainability and social safeguards

GBF pathways involving biomass must adopt CORSIA SAF rules to prohibit conversion from land with high carbon stock or high biodiversity. The report recommends following Article 6.4 best practices to avoid the conversion of culturally and environmentally relevant land and to survey impacts on the livelihoods of affected communities. Social safeguards should also be inspired by Article 6.4 provisions to protect labour, gender, and human rights, ensuring that benefits are robustly shared with local communities and aligned with Sustainable Development Goals.

Governance and scalability

Governance provisions must ensure the certification framework is institutionally credible and publicly accountable. GBF project developers should demonstrate financial security sufficient to cover long-term storage obligations. The report recommends establishing a structured methodology development and review process, including scientific advisory input and public comment periods. Finally, GBF certification should seek formal recognition under schemes like ReFuelEU and the EU ETS to reduce administrative duplication for multi-jurisdictional fuel suppliers.