How the main sustainability assurance standards differ: ISO 14064-3 for GHG verification, ISAE 3000 until the end of 2026, and ISSA 5000 from FY2027, and when each applies.
Part of the reading list: GCC and Jordan ESG disclosure
Introduction
“Get the report assured” sounds simple until someone asks: assured against which standard? Three standards matter for GCC companies: ISO 14064-3, ISAE 3000 and ISSA 5000. Choosing the wrong one wastes money or weakens the report. This article explains how they differ, when each applies, and how the arrival of ISSA 5000 changes the choice from FY2027.
The three standards at a glance
| Standard | Subject matter | Issued by | Status for sustainability information |
|---|---|---|---|
| ISO 14064-3 | Greenhouse gas statements | ISO | Continues |
| ISAE 3000 (Revised) | Any subject matter other than historical financial information | IAASB | Applies to periods beginning before 15 December 2026 |
| ISSA 5000 | Sustainability information of any kind, including GHG | IAASB | Applies to periods beginning on or after 15 December 2026, early application permitted |
In short: ISO 14064-3 is the GHG verification standard, ISAE 3000 was the IAASB’s general route for sustainability assurance, and ISSA 5000 replaces it for sustainability information from FY2027.
ISO 14064-3: the GHG verification standard
ISO 14064-3 sets out how to validate and verify greenhouse gas statements: organisational inventories, projects and product footprints. Accredited verification bodies work to it, and it is the natural fit when the subject matter is purely emissions, such as a GHG inventory or a CBAM verification. It is an ISO standard, so the IAASB’s changes do not affect it.
ISAE 3000: the general standard, until 2026
ISAE 3000 (Revised) is the IAASB’s general assurance standard for subject matter other than historical financial information. For years it has been the default for sustainability reports and ESG KPIs, at both limited and reasonable assurance.
That changes with ISSA 5000. The IAASB’s August 2025 FAQ states that ISAE 3000 (Revised) will no longer be applicable for sustainability assurance engagements after ISSA 5000’s effective date. It remains in use for other non-financial subject matter. ISAE 3410, the IAASB standard for greenhouse gas statements, is withdrawn from the same date.
ISSA 5000: the dedicated standard from FY2027
ISSA 5000 is the IAASB’s standard written specifically for sustainability assurance, usable with any suitable framework, including IFRS S1 and S2, GRI and ESRS. It applies to sustainability information reported for periods beginning on or after 15 December 2026, so FY2027 for a calendar-year company, and may be applied earlier. Accountants and other practitioners can both use it, provided they meet the IESBA ethics and independence standards and ISQM 1, or equivalents.
In the GCC, Saudi Arabia’s SOCPA and Oman’s OACPA have adopted it, and Qatar’s securities regulator references it for the assurance of listed companies’ sustainability reports. See ISSA 5000 in the GCC.
The question is rarely “ISO or ISAE or ISSA.” It is: what exactly am I assuring, for which period, for whom, and to what level of confidence?
How to choose
Four questions decide it:
- What is the subject matter? A GHG statement points to ISO 14064-3. A sustainability report or a set of ESG metrics points to an IAASB standard.
- Which reporting period? For periods beginning before 15 December 2026, ISAE 3000 or early application of ISSA 5000. From then on, ISSA 5000.
- Who expects what? Regulators, lenders and exchanges increasingly name ISSA 5000. Qatar’s QFMA already does.
- What level of confidence? Limited or reasonable. Our article on limited versus reasonable assurance under ISSA 5000 explains the difference in work.
For most GCC companies the answer combines standards rather than picking one.
How ESGweise helps
ESGweise delivers assurance under ISSA 5000 and ISAE 3000 and GHG verification under ISO 14064-3, matching the standard to the subject matter and the period, scoping limited or reasonable assurance, and building the evidence files that let the report stand up. See our assurance practice.
Conclusion
ISO 14064-3, ISAE 3000 and ISSA 5000 are tools for different jobs. From FY2027, ISSA 5000 takes over from ISAE 3000 for sustainability information, while ISO 14064-3 continues for GHG verification. Knowing which applies to which subject matter and period is the difference between assurance that reassures and assurance that wastes money.
Related reading
The ISSA 5000 series: what the standard is and when it applies, materiality and a readiness checklist for companies. Our other ISO guides cover ISO 14083 transport and logistics emissions and ISO 59000 circular economy standards. For implementation support, see our ISO implementation service.
Sources
- IAASB, ISSA 5000, General Requirements for Sustainability Assurance Engagements, November 2024, paragraph 15.
- IAASB staff, FAQ: Applicability of ISSA 5000, ISAE 3000 (Revised) and ISAE 3410, August 2025.
- IAASB, Understanding ISSA 5000, Jurisdictional Adoption Details updated September 2026, checked 24 October 2026.
Frequently asked questions
What is the difference between ISO 14064-3, ISAE 3000 and ISSA 5000?
ISO 14064-3 is an ISO standard for validating and verifying greenhouse gas statements. ISAE 3000 (Revised) is the IAASB's general assurance standard for subject matter other than historical financial information, and has been the usual standard for sustainability reports. ISSA 5000 is the IAASB's standard written specifically for sustainability assurance. For periods beginning on or after 15 December 2026 it replaces ISAE 3000 for sustainability information.
When does ISSA 5000 take effect?
For assurance engagements on sustainability information reported for periods beginning on or after 15 December 2026, or as at a specific date on or after that date, with early application permitted. For a calendar-year company the first year in scope is FY2027.
Can ISAE 3000 still be used after ISSA 5000 takes effect?
Not for sustainability information, under IAASB standards. The IAASB's August 2025 FAQ states that ISAE 3000 (Revised) will no longer be applicable for sustainability assurance engagements after ISSA 5000's effective date. In a jurisdiction that has adopted ISAE 3000 but not yet ISSA 5000, practitioners may keep using ISAE 3000, but cannot then claim compliance with IAASB standards for that engagement. ISAE 3410 for GHG statements is withdrawn from the same date.
Which assurance standard should a GCC company choose?
For a GHG inventory or CBAM-related verification, ISO 14064-3. For a sustainability report or selected ESG metrics for FY2027 onward, ISSA 5000. For FY2026 reports, ISAE 3000 remains available, and ISSA 5000 may be applied early. Many engagements combine ISO 14064-3 verification of the emissions data with an assurance engagement on the wider report.
What is the difference between limited and reasonable assurance?
Limited assurance is substantially lower than reasonable assurance, with procedures that are less in extent, and a conclusion stating whether anything has come to the assurer's attention. Reasonable assurance is a high level of assurance, equivalent to a financial statement audit, with a positive opinion. All three standards can deliver both levels.