How to Write an RFP for a Corporate Greenhouse Gas Inventory

The California Air Resources Board’s March 2026 workshop cited a survey of 497 companies in which 42.9% disclosed no Scope 3 category at all. The most common category, business travel, was reported by fewer than half. Regulation is closing that gap one category at a time, and a buyer who writes a vague inventory RFP in 2026 will pay to redo it in 2027.

A corporate greenhouse gas inventory measures an organization’s Scope 1, 2 and 3 emissions for a fiscal year under the GHG Protocol. You need one for disclosure laws such as California’s SB 253, customer requests, targets or a transition plan. The RFP succeeds when it fixes the boundary, the data owners and the audit trail before anyone calculates.

What this work should deliver

The outcome is an inventory that an assurance provider can test and that management can act on. That means a boundary memo, calculation files that trace every number to a source document, a data management plan naming who owns each input, and a recalculation policy. Our guide on how to calculate a carbon footprint covers the arithmetic; the RFP has to buy the controls around it.

Decide four things before you write tasks:

• Organizational boundary. Equity share or control, and which entities, leases and joint ventures that captures.
• Uses. SB 253, the CSRD (where a double materiality assessment decides what else you report), customer questionnaires, a science-based target or internal decisions. Each adds requirements.
• Scope 3 depth. A screen of all 15 categories first, then deeper work where emissions or rules concentrate.
• Assurance readiness. Whether the first year must survive an outside review.

Who this is for. Sustainability, finance and operations staff at companies, utilities, ports, universities and public agencies measuring their own footprint. It is the wrong template for a city’s community-wide emissions (see our community inventory RFP guide), a product life cycle assessment, or a full annual report (see the sustainability report RFP guide).

Rules and standards to cite

GHG Protocol. The Corporate Standard requires companies to report Scope 1 and Scope 2 at a minimum, lets them consolidate by equity share or control, and requires a base-year recalculation policy with any significance threshold stated. The Scope 2 Guidance requires "dual reporting" by the location-based and market-based methods wherever contractual instruments exist, and its page lists eight quality criteria those instruments must meet. The Scope 3 Standard says companies "shall account for all scope 3 emissions and disclose and justify any exclusions."

Revision status, September 2026. GHG Protocol consulted from October 20, 2025 to January 31, 2026 on hourly matching and deliverability for market-based Scope 2. On July 29, 2026 it published the feedback and announced a consolidated standard with ISO 14064-1: public consultation in the second quarter of 2027, publication in the fourth quarter of 2028. Until then, the 2015 guidance applies.

California SB 253. Health and Safety Code section 38532 covers U.S.-formed entities with more than $1 billion in revenue that do business in California. It requires conformance with the GHG Protocol, phases in limited then reasonable assurance (from 2030), caps penalties at $500,000 per reporting year, and shields Scope 3 misstatements made with a reasonable basis and in good faith. The rest of the picture:

• CARB’s final regulation order sets November 10, 2026 for Scope 1 and 2 reports, allows consolidation at the parent level and requires no Scope 3 this year. CARB resubmitted it to the Office of Administrative Law on September 21, 2026.
• For 2026 only, companies may report what they could determine from data they held or were collecting by December 5, 2024, the date of CARB’s enforcement notice. CARB’s November 2025 workshop confirmed that limited assurance is not required for 2026 reports.
• CARB’s July 2026 proposal for 2027 onward would require five Scope 3 categories, limited assurance of Scope 1 and 2 under standards including ISO 14064-3:2019 and ISSA 5000, dual Scope 2 reporting and disclosure of every exclusion with an estimate of its size where quantifiable. It is a proposal, not a rule.

Elsewhere. The SEC’s 2024 climate rule never took effect, and the SEC proposed rescinding it on May 29, 2026. In the EU, the CSRD now covers EU companies with more than 1,000 employees and more than €450 million in net turnover, per the European Parliament, and the revised ESRS apply from financial years beginning January 1, 2027, per the Commission. ESRS E1 asks for gross Scope 1, 2 and 3 emissions. Facilities in EPA’s reporting program filed 2025 data on an extended October 30, 2026 deadline, and those filings should reconcile with your Scope 1.

Sample scope of work

Seven tasks cover a first inventory. The first and the last are the ones buyers leave out.

Task 1. Boundary and methods memo.

Within 30 days of notice to proceed, the Consultant shall deliver a memo stating the consolidation approach, the entities, facilities, leases and joint ventures included, the base year, the gases and global warming potential values, emission factor sources and vintages, and each intended use of the inventory, with the requirements each use adds. No calculations shall begin before the [Company] approves the memo.

Task 2. Scope 1 and 2.

The Consultant shall calculate Scope 1 emissions by source and Scope 2 emissions by the location-based and market-based methods, document every contractual instrument against the Scope 2 quality criteria, and collect interval or hourly electricity data where meters provide it.

Asking for hourly data now is cheap insurance. The consultation draft on hourly matching may change market-based accounting in the consolidated standard, and data you never collected can’t be restated. See our comparison of market-based and location-based methods.

Task 3. Scope 3 screen and priority categories.

The Consultant shall screen all 15 Scope 3 categories using spend and activity data, document the basis for any exclusion with an estimate of its size, and calculate in detail the categories that are largest or required by [SB 253 or other programs], stating the method and data quality for each.

Our guide on how to measure Scope 3 emissions explains the category methods.

Task 4. Supplier data. Target the few suppliers that matter.

The Consultant shall identify the suppliers responsible for [the top 70 percent] of screened Category 1 emissions, prepare a data request and support the [Company] in collecting supplier-specific data, and report which results use supplier data and which use averages.

In our work with Luke’s Lobster, the Scope 1, 2 and 3 analysis for its two main products, lobster and crab, meant assessing a lobsterman-based supply chain, and the work focused on recommendations that were actionable and culturally sensitive. That is a scoping point as much as a method point.

Task 5. Base year and recalculation policy.

The Consultant shall recommend a base year and a written recalculation policy, including a significance threshold, for structural changes, method changes and errors.

Task 6. Controls and assurance readiness.

The Consultant shall deliver an inventory management plan with data owners, collection calendars, quality checks, evidence files for each data point and a mock assurance walkthrough with [Company] staff. The Consultant shall not provide assurance on the inventory it prepares.

Task 7. Reporting and handoff.

The Consultant shall prepare the [SB 253 submission, CDP response and public summary], map results to [ESRS E1 or other frameworks], and train staff to run the next annual update from the delivered files.

Deliverables to require

• Boundary and methods memo, approved before calculations.
• Calculation workbook with activity data, factors with vintages, global warming potential values and formulas visible.
• Scope 2 results by both methods, with an instrument register.
• Scope 3 screening of all 15 categories, exclusion rationale with estimated size, and detailed results for priority categories.
• Supplier data log showing which results use supplier-specific data.
• Base-year statement and recalculation policy.
• Inventory management plan, evidence files and a mock assurance readout.
• Draft regulatory submissions and a plain-language summary for leadership.
• Training session and a written procedure for the annual update.

How to evaluate proposals

Keep preparation and assurance in separate contracts. CARB’s July 2026 proposal calls for an independent third-party assurance provider, and a firm cannot credibly test its own workbook. If your organization is public, check your procurement rules; the Port of Bellingham’s 2025 RFP capped proposals at 20 pages, which rewards specifics.

Ask each finalist to trace one number, such as a facility’s natural gas emissions, from invoice to report in the interview. It shows whether the audit trail exists or will be assembled later.

Timeline

New York’s guidance puts a first inventory at up to a year and later updates at a few months. The phase durations below are suggested allocations within that range.

The New York guidance, written for government operations inventories, adds a scoping rule worth borrowing: an inventory covering about 95% of emissions is acceptable under the local government protocol. The Port of Bellingham shows the cadence. It had inventories for 2019, 2022 and 2023, added vessels to Scope 3 in 2023 and is weighing tenants’ energy and maritime customers next.

Budget and cost drivers

The best public benchmark comes from CARB. Its March 2026 analysis, adapted from SEC rulemaking data that included a survey of 39 companies, estimated these average annual costs per company:

• Scope 1 and 2 reporting: $82,278.
• Scope 3 reporting: $8,635 to $25,904, depending on the option.
• Limited assurance of Scope 1 and 2: $44,170.
• Total: $135,083 to $152,352, with first-year costs higher.

These estimate a large company’s whole reporting cost, from data collection and inventory building to report preparation and assurance, so a consultant’s fee is only one part. CARB’s July 2026 slides add that costs vary with size and complexity, existing systems and in-house expertise, access to assurance providers and prior Scope 3 experience.

What moves the consultant’s price:

• The number of entities, facilities and countries inside the boundary.
• Whether utility, fuel and refrigerant data sit in one system or in site files.
• Scope 3 depth: spend-based screening costs far less than supplier-specific data.
• Contractual instruments that need documentation against the quality criteria.
• The number of frameworks the results must map to.
• Assurance readiness work, which is separate from the assurance fee.

Red flags in proposals

• Offers to prepare and assure the same inventory.
• Skips the boundary memo, or treats leased assets and joint ventures as a detail.
• Reports only one Scope 2 method.
• Picks Scope 3 categories without a screen of all 15, or excludes categories without an estimate of their size.
• Uses emission factors without stating their source and vintage.
• Delivers results in a locked platform with no exportable workbook.
• Promises "carbon neutral" claims from the first inventory.

How we’d approach it

We’d treat the inventory as the start of a reduction plan, not the end of a reporting exercise. In our work with Luke’s Lobster on its path to carbon-neutral operations, the analysis identified reductions the company could make right away and others to phase in over the coming years, and it fed a plan for engaging fishermen, regulators and supply chain partners. The GHG Protocol guide and our SB 253 guide cover the rules in more depth, and the sustainability assurance guide covers the separate assurance contract.