Define: CAS number

What CAS number Means in a Contract

A CAS number, formally a CAS Registry Number, is a unique numeric identifier assigned by the Chemical Abstracts Service to a distinct chemical substance, mixture, polymer, or biological sequence. In a contract, referencing a CAS number allows the parties to identify precisely which chemical is being supplied, handled, stored, or regulated, without relying solely on a product name, trade name, or generic chemical description that could be interpreted differently by each party.

Contracts that involve the sale, manufacture, storage, or transport of chemical substances often use CAS numbers as a shorthand for accuracy. Because chemical names can vary by language, industry convention, or manufacturer branding, the CAS number functions as a stable cross-reference point that both parties, and any regulator reviewing the agreement, can rely on to confirm exactly what substance is covered.

This use of CAS numbers is particularly common in supply agreements, manufacturing contracts, and safety documentation attached to commercial agreements in the Manufacturing and chemical distribution sectors, where the risk of substituting or misidentifying a substance can carry significant safety, regulatory, or liability consequences.

How CAS number Is Defined or Measured

A CAS number is not measured in the sense of a quantity or standard; rather, it is an assigned identifier. The Chemical Abstracts Service maintains a registry that links each unique chemical structure to a specific number, following a defined format that typically consists of up to ten digits separated by hyphens. Once assigned, a CAS number is permanently associated with that substance and is not reused for a different compound.

In a contractual context, the definition of a CAS number typically references the substance description provided by the CAS registry itself, rather than any internal company naming convention. Parties drafting a contract will often state that, in the event of any inconsistency between a product name and its associated CAS number, the CAS number will control, because it offers a more precise and internationally recognizable reference than a brand or trade name.

• The identifier is purely numeric and hyphenated, without any inherent chemical meaning encoded in the digits themselves.
• It applies to a specific substance, not a category, mixture proportion, or formulation unless that mixture itself has been separately registered.
• It remains constant regardless of the manufacturer, supplier, or trade name under which the substance is sold.

Where CAS number Appears in Agreements

CAS numbers most frequently appear in schedules, exhibits, or specification annexes attached to supply, distribution, or manufacturing contracts. Rather than sitting in the main body of an agreement, the CAS number is typically listed alongside other technical details such as concentration, grade, purity, or packaging requirements, forming part of the product specification that the parties are contractually bound to meet.

They also appear in safety data sheet references, regulatory compliance clauses, and representations and warranties sections where a supplier confirms that the substances delivered match an agreed list of CAS numbers. In service agreements involving handling, testing, or disposal of chemical substances, CAS numbers may be used to define the scope of services being performed on a particular substance.

Industries such as Energy and construction materials supply also rely on CAS numbers within environmental compliance schedules, where a contract may require that any substance bearing a listed CAS number be reported, restricted, or handled according to specific procedures.

Why the Exact Wording Matters

Precision in referencing a CAS number matters because even a small transcription error, such as a transposed digit, can result in the parties unintentionally referring to an entirely different chemical substance. This can create serious consequences in agreements governing hazardous materials, pharmaceuticals, or regulated industrial chemicals, where the wrong substance being delivered or referenced could trigger safety incidents or breach of the law governing the contract.

Clear wording also helps resolve conflicts between a product's marketing name and its underlying chemical identity. If a contract states that the CAS number governs in case of discrepancy with any trade name or product code, the parties reduce the risk of disputes over which substance was actually intended to be supplied or regulated under the agreement.

Additionally, many regulatory frameworks require accurate CAS number reporting for import, export, hazardous waste, or safety labeling purposes. If a contract's wording is vague or omits the CAS number altogether, the parties may struggle to demonstrate compliance to regulators or during an audit.

Drafting Considerations

When drafting or reviewing a contract that references CAS numbers, it is important to confirm that the numbers cited are current and correctly matched to the intended substance, since registry records are the authoritative source. Simply copying a CAS number from an old specification sheet without verification can introduce errors that persist through multiple contract renewals.

Drafters should also consider whether the contract needs a precedence clause stating that the CAS number controls over any conflicting product name, and whether updates to CAS numbers or substance reclassification should trigger a formal amendment process rather than a unilateral update by one party.

Finally, parties operating across multiple jurisdictions should be mindful that reporting obligations tied to CAS numbers can differ from the law governing the contract in another jurisdiction, so cross-referencing internal compliance schedules with the specific CAS numbers used in the agreement is a prudent step, particularly for organizations in Healthcare or chemical manufacturing where substance identity carries heightened regulatory scrutiny.