CORSIA Carbon Credits: What Airlines Need to Know Before the 2027 Mandatory Phase

Understanding CORSIA eligibility, supply constraints, and sourcing strategy ahead of the scheme’s mandatory phase. 

In 2024, international aviation emissions exceeded the CORSIA baseline for the first time, triggering the scheme’s first real offsetting obligations. This was the start of enforceable compliance requirements for airlines operating between participating states. As of 2026, 130 states voluntarily participate in the first phase, and ICAO lists 134 states participating from January 1, 2027. As the scheme’s mandatory second phase approaches in 2027, airlines should start to build a CORSIA-eligible credit sourcing strategy now, before demand rises and eligible supply tightens further. 

This article breaks down how CORSIA works, what the primary constraint airlines face today is, and what a compliant sourcing strategy needs to account for heading into the next compliance period. 

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What is CORSIA? 

CORSIA, the Carbon Offsetting and Reduction Scheme for International Aviation, is a mechanism developed by the International Civil Aviation Organization (ICAO) to cap the net growth of international aviation emissions. Airlines operating flights between participating countries are required to offset emissions that exceed a baseline set at 85% of 2019 CO2 levels. 

The scheme is being implemented in three phases: 

• Pilot phase (2021–2023): Voluntary participation; no offsetting requirements were triggered, as the sector growth factor remained at zero throughout the pandemic recovery period. 

• First phase (2024–2026): Still voluntary at the country level, but airlines in participating states now face real, calculated offsetting obligations. 

• Second phase (2027–2035): Participation becomes mandatory for most ICAO member states, with exemptions for least-developed countries, small island developing states, landlocked developing countries, and states that fall below ICAO’s aviation-activity thresholds based on 2018 Revenue Tonne Kilometers (RTKs). 

According to ICAO, the 2024 sector’s growth factor was calculated at approximately 15.4 -15.9%, translating to a global offsetting requirement of roughly 55–58 million tonnes of CO2 for that year. Across the full first phase, IATA and independent market analysts project total demand for CORSIA-eligible credits in the range of 146 to 236 million tonnes. 

What Makes a Carbon Credit CORSIA-Eligible? 

Not every carbon credit qualifies for CORSIA compliance, even from a reputable registry. To count toward an airline’s offsetting obligation, a credit must come from a program ICAO’s Technical Advisory Body has approved for that compliance period, and the underlying project must meet additional criteria around crediting period, vintage, host-country authorization, and methodology. 

For airlines, the takeaway is simple: a credit can be high-quality on the general voluntary market and still fall outside CORSIA’s eligibility filters. Sourcing for regulatory compliance is a different exercise from sourcing for a broader sustainability portfolio, with its own risk considerations. 

Why Supply Is the Real Constraint 

Much of the conversation around CORSIA compliance focuses on credit pricing. In practice, the more pressing issue for airlines today is the limited supply of credits that have cleared every eligibility hurdle required for use. 

Before a host country's carbon credits can be used for CORSIA compliance, that country must authorize their use for CORSIA and ensure the same reductions are not also counted toward its own nationally determined contribution (NDC) under the Paris Agreement. In practice, this is handled through a Letter of Authorization and corresponding adjustment process. This is a significant policy decision for host governments, and as of April 2026, IATA reported that 10 countries had supplied CORSIA Eligible Emissions Units through Letters of Authorization. Guyana was the first, authorizing more than 15 million ART TREES credits from its jurisdictional REDD+ program in 2024, an issuance that remains the benchmark case for the market. 

The result is that eligible supply remains concentrated, even though multiple registries and standards have broad approval. Airlines that wait until later in the compliance period to secure credits may find themselves competing for a narrow pool of genuinely eligible units, rather than facing a straightforward pricing negotiation. 

Pricing is expected to climb as Phase 1 draws to a close, and airlines face a hard deadline to transact for compliance. That end-of-period crunch tends to compress negotiating leverage: buyers need units on a fixed timeline, and sellers know it. Current pricing, by comparison, reflects the real cost structure behind these credits; project implementation, obtaining Letters of Authorization from host countries, insurance, and the verification and monitoring that goes into keeping a unit eligible. Airlines securing credits now are effectively paying for that underlying cost base. 

What Airlines Should Be Tracking Ahead of the Second Phase 

A few developments are worth building into any airline's compliance planning, regardless of where the organization currently stands: 

• Second-phase eligibility criteria are already taking shape. ICAO's April 2026 eligible-units document includes approvals for the 2027-2029 compliance period for American Carbon Registry, Architecture for REDD+ Transactions, Gold Standard, and Verra's Verified Carbon Standard. However, eligibility is still program- and scope-specific, and additional program assessments may continue. Credits eligible today may not automatically carry over. 

• Overlapping regional schemes add complexity. On July 17, 2026, the European Commission completed its assessment of CORSIA and concluded the scheme still falls short of the coverage threshold that would legally require folding all departing flights into the EU Emissions Trading System (ETS). Rather than a full expansion, the Commission's proposal keeps the EU's existing CORSIA implementation in place and limits added ETS scope to near-neighborhood routes of 5,000 km or less, starting in 2029, with a further review planned for 2032. Airlines flying both intra-European and near-neighborhood routes should watch how this proposal moves through the EU legislative process, since the split between CORSIA and ETS coverage is drawn by route distance rather than emissions. 

• Documentation and traceability matter as much as the credit itself. Given the scrutiny CORSIA-eligible credits face, airlines should be prepared to demonstrate not just that a credit came from an approved program, but that the specific project, vintage, and host-country authorization all meet current eligibility requirements. 

How CarbonBetter Supports Airlines with CORSIA Compliance 

Sourcing CORSIA-eligible credits requires navigating registry-level approvals, project-level eligibility restrictions, and host-country authorization status simultaneously, an evaluation process most airlines aren't set up to manage internally on an ongoing basis. CarbonBetter works with airlines to build compliance-ready credit portfolios, track authorization progress across host countries, and plan sourcing ahead of the second phase, rather than reacting to it. 

We have deep relationships with 40+ developers across the globe and access to several competitively priced CORSIA credits to build robust carbon credit portfolios. Not sure where to begin? Contact us and get expert help to guide you so you can buy the best carbon credits for your goals. Carbon Better sources quality offsets for you so you will get the most out of your purchase and help you transition to a net-zero future.