The GHG Protocol's own guidance is built around prioritisation rather than uniform coverage: prioritise the activities that matter, collect primary data there, and use secondary data elsewhere. Segmenting suppliers is how a procurement team puts that into practice.
Summary
- The GHG Protocol directs companies to prioritise scope 3 activities first, then collect high quality primary data for high priority activities.
- It explicitly allows selecting suppliers by their contribution to total spend, and directs companies to engage tier 1 suppliers first.
- Secondary data is the standard's expected answer for activities that are not prioritised, or where a supplier cannot provide data of sufficient quality.
- Companies are required to disclose the percentage of emissions calculated using supplier data, which makes segmentation decisions visible.
- EU law now limits how much can be demanded from smaller suppliers, which makes tiering a practical necessity rather than a courtesy.
Why Uniform Questionnaires Fail
A supplier's capability to report is not related to how much you buy from them. Sending one questionnaire to everyone produces blank fields from the suppliers who cannot answer and low-value responses from the ones who do not matter to your footprint.
Duplication across buyers compounds it, though the scale needs stating accurately. EFRAG's secretariat analysed 12 real ESG questionnaires covering roughly 26,000 SMEs, issued under initiatives spanning around 700 banks and 450 value chain companies. Energy and greenhouse gas emissions were requested in all 12; water and waste in nine each efrag.org.
That is duplication between instruments, not proof that every supplier answers a dozen forms. EFRAG found most SMEs received a single request in 2023. The pressure is directional: as obligations widen, the same overlapping questions arrive through more channels, which is why the EU legislature recorded that value chain companies receive disproportionate requests for information.
What the GHG Protocol Says About Prioritisation
The standard does not ask for universal coverage. It asks for a sequence.
Companies should prioritise scope 3 activities first, then select data based on business goals, the relative significance of each activity, and the availability and quality of data. In general, companies should collect high quality primary data for high priority activities, and specifically for the activities targeted for emissions reductions, because that is what allows performance to be tracked ghgprotocol.org.
On which suppliers to approach, the standard is direct. Companies should first engage relevant tier 1 suppliers, those with a purchase order relationship, because that relationship provides the leverage needed to request inventory data.
It also notes that a company may have many small tier 1 suppliers that together comprise only a small share of total spending, and that companies may set their own policy for selecting targets, for example by contribution to total spend.
The GHG Protocol's Supplier Engagement Guidance puts a number on it. As a general rule of thumb, companies should request data from the top 80% of known suppliers based on a preliminary evaluation of emissions contribution or spend, with that share expected to grow over time ghgprotocol.org.
It also notes that suppliers reporting for the first time may need additional guidance, which is a segmentation input in its own right.
Where secondary data is the correct answer
This is the half of the guidance most often dropped, and it is what keeps a segmentation model defensible.
The standard states that in some cases primary data may not be available or may not be of sufficient quality, and that in such cases secondary data may be of higher quality than the available primary data.
It directs companies to collect secondary data for activities not prioritised, activities where primary data is not available because a value chain partner is unable to provide it, and activities where secondary data quality is simply higher.
Excluding a supplier from primary data collection is therefore not a gap in the inventory. It is the method the standard expects, provided the choice is disclosed.
Two Axes for Segmenting a Supplier Base
Segmentation works when it separates the question of who matters from the question of who can answer.
The axis most procurement teams get wrong is the second one. Reporting capability is not a proxy for supplier quality or commitment; it usually reflects whether the supplier has ever had a reason to build the capability.
What to Ask Each Segment
The standard sets out what a buyer may reasonably request from a supplier: Scope 1 and 2 emissions for the reporting year, a description of the methodologies and data sources used including emission factors, the allocation method applied or the information needed for the buyer to allocate, and whether the data has been assured and to what level.
For a high-capability supplier in a priority category, that full set is a reasonable ask. For a small supplier with no sustainability function, requesting the same thing produces guesses. The GHG Protocol's specificity hierarchy gives the fallback order: product-level data if available, then activity or production line-level, then facility, business unit, and corporate-level.
What Regulation Is Doing to This
The direction of travel in the EU is towards limiting what buyers can demand from smaller suppliers, not expanding it.
The European Commission's 2025 recommendation on voluntary SME reporting describes the trickle-down effect, whereby companies subject to reporting requirements request sustainability information from value chain companies that are not, and aims to reduce the need for SMEs to answer separate requests from individual counterparties eur-lex.europa.eu.
Directive (EU) 2026/470 makes that a right. It records evidence that value chain companies including SMEs receive disproportionate requests for information, and provides that companies averaging 1,000 employees or fewer in a reporting company's value chain may decline to provide information exceeding the voluntary standard eur-lex.europa.eu.
A procurement team that has already tiered its supplier base is positioned for that. One relying on a single exhaustive questionnaire is not.
Where Singapore currently stands
For buyers listed in Singapore, the binding instrument is the SGX rulebook. Listing Rules 711A and 711B, with the sustainability reporting guide in Practice Note 7.6, set what issuers must report rulebook.sgx.com.
Timing changed in 2025. ACRA and SGX RegCo announced adjustments to the climate reporting roadmap in August 2025 acra.gov.sg. One point is worth stating plainly, because it is often reported as settled: the obligation trailed for large non-listed companies is an announced roadmap, not enacted law.
Enabling legislation is still being prepared and the Singapore standards remain in consultation. Today, only listed issuers sit under a binding requirement.
For a procurement team, the practical read is that supplier data requests will keep arriving from listed customers now, and from a wider set later. Build the segmentation for the wider set, but do not tell suppliers they face an obligation that does not yet exist.
How to Measure Progress
The GHG Protocol requires companies to report a description of the types and sources of data used, and the percentage of emissions calculated using data obtained from suppliers or other value chain partners. That percentage is the natural progress measure for a segmentation programme, because it moves only when priority suppliers actually start reporting.
Coverage counted as a share of suppliers contacted is the wrong measure. It rises when you send more questionnaires, including to suppliers whose data would not change the inventory.
Frequently Asked Questions
How many tiers should a segmentation model have?
No standard prescribes a number. What the GHG Protocol requires is that prioritisation is deliberate and that the resulting data sources are disclosed. Two axes, significance and reporting capability, are usually enough to drive different treatment.
Should low-significance suppliers be excluded from data collection entirely?
They should generally be covered with secondary data rather than a questionnaire. The standard directs companies to use secondary data for activities that are not prioritised.
Is supplier-reported data always better than secondary data?
No. The standard states that secondary data may be of higher quality than the available primary data where a supplier cannot provide data of sufficient quality. Data quality is assessed on representativeness in technology, time and geography, plus completeness and reliability.
Which suppliers should be approached first?
Tier 1 suppliers in priority categories. The standard notes the purchase order relationship provides the leverage to request inventory data, and that suppliers may be selected by contribution to total spend.
About Gprnt
Gprnt is sustainability data infrastructure launched by the Monetary Authority of Singapore (MAS) and operated by the Global Finance & Technology Network (GFTN), open digital infrastructure accessible to businesses of every size.
Its Value Chain Intelligence pillar connects enterprise buyers with supplier-reported ESG data across procurement and financing. Entry-level Scope 1 and 2 reporting is free for SMEs, which is what makes participation realistic for the smaller suppliers a segmentation model would otherwise have to leave on secondary data.
To see how supplier data collection works across a tiered supplier base, visit gprnt.ai.
References
- GHG Protocol, Corporate Value Chain (Scope 3) Accounting and Reporting Standard, sections 7.1, 7.3 and 7.4 (ghgprotocol.org)
- GHG Protocol, Technical Guidance for Calculating Scope 3 Emissions (ghgprotocol.org)
- GHG Protocol, Supplier Engagement Guidance (ghgprotocol.org)
- SGX Rulebook, Practice Note 7.6 Sustainability Reporting Guide (rulebook.sgx.com)
- ACRA and SGX RegCo announcement on climate reporting timelines (August 2025) (acra.gov.sg)
- EFRAG, VSME Exposure Draft Basis for Conclusions (January 2024), BC44 and BC45 (efrag.org)
- Commission Recommendation (EU) 2025/1710 on a voluntary sustainability reporting standard for SMEs (eur-lex.europa.eu)
- Directive (EU) 2026/470 (eur-lex.europa.eu)