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SB253 Vendors

Guide

Questions to ask when evaluating GHG accounting, data and assurance vendors

Last reviewed: September 20, 2026

This is a general due-diligence checklist, not legal, accounting or regulatory advice, and it is not a ranking or recommendation of any vendor. SB253 Vendors does not test or score vendors. Adapt the questions to your situation.

Start with what you need

Write down which scopes you need to measure, which reporting frameworks you use, whether you need software, data, advisory help or assurance, and who inside your company will own the process. Vendor categories overlap, so a clear scope makes comparisons meaningful.

Questions for software and platform vendors

  • Which GHG accounting standards does the product's methodology follow, and can the vendor show documentation?
  • Which emission factor sources and versions are used, and how are updates handled?
  • Can you trace any reported figure back to its source data, calculation and factor?
  • Which Scope 3 categories are supported, and how are activity data and spend-based estimates handled?
  • Who owns the data, and can you export everything in a usable format if you leave?
  • What security reports or certifications does the vendor hold, and can it share the reports under NDA?
  • What is the pricing structure, including implementation, data volume and add-ons?
  • Can the vendor provide references from companies of similar size and industry?

Questions for consultants

  • Who will actually do the work, and what is their GHG inventory experience?
  • What deliverables and timelines are included, and what is excluded?
  • If the firm also offers assurance, how does it manage independence between advisory and assurance work?

Questions for assurance providers

  • Which assurance standards does the provider use, and are they the ones your reporting requirements name?
  • Is the provider accredited for GHG verification, by which body, for which scope, and until when? Confirm in the accreditor's own directory.
  • What experience does the engagement team have with your industry and with your scopes?
  • What is the engagement timeline, and what evidence will the team need from you?
  • Does the provider or an affiliate also provide the software or consulting services you use?

Red flags

  • Claims that a vendor is "SB 253 approved," "CARB approved" or guarantees compliance. As of September 20, 2026 we found no CARB list of approved vendors. Ask for the source of any such claim.
  • Claims without sources or dates, such as certifications or accreditations that cannot be checked with the issuing body.
  • Pressure to buy before you have defined your scope.
  • Unclear data ownership or export terms.

Sources