What is the on-sale bar in patent law?

The on-sale bar is a patent law doctrine that prevents an inventor from obtaining patent protection for an invention that was placed on sale before a statutory cutoff date tied to the patent application's effective filing date. It is one of the most significant and underestimated triggers of patent loss, because it can attach quietly through ordinary commercial activity long before a practitioner is engaged.

Statutory basis

Under AIA 35 U.S.C. § 102(a)(1), a claimed invention is not patentable if it was "on sale" before the effective filing date. The on-sale bar is one of several prior art categories in that provision alongside patents, printed publications, public use, and subject matter otherwise available to the public.

The Pfaff two-part test

The Supreme Court in Pfaff v. Wells Electronics, Inc. established the governing framework: the on-sale bar applies when (1) the invention is the subject of a commercial offer for sale, not primarily for experimental purposes, and (2) the invention is ready for patenting. Both prongs must be satisfied before the statutory cutoff date for the bar to attach.

First prong: commercial offer for sale

A commercial offer for sale requires an offer that rises to the level where the other party could make it into a binding contract by simple acceptance, including material terms such as pricing, quantities, delivery terms, and product specifications. A preliminary inquiry, a request for quotation, or a communication that lacks material binding terms does not constitute a commercial offer for sale sufficient to trigger the bar.

Actual delivery of goods is not required for the bar to attach, and even a rejected commercial offer, never consummated, can trigger the bar once the threshold of a commercial offer is met.

Second prong: ready for patenting

The ready-for-patenting prong is satisfied by either actual reduction to practice before the critical date, or proof that the inventor had prepared drawings or other descriptions of the invention sufficiently specific to enable a person skilled in the art to practice the invention.

This means the bar can attach well before a working prototype exists. In Pfaff itself, detailed engineering drawings sent to a manufacturer were sufficient to satisfy the ready-for-patenting prong even without a completed physical embodiment.

Confidential sales count

A frequently misunderstood aspect of the on-sale bar is that the transaction does not need to be public to trigger the bar. The Supreme Court in Helsinn Healthcare S.A. v. Teva Pharmaceuticals USA, Inc. held unanimously that a sale made to a third party under a confidentiality agreement can constitute prior art under AIA § 102(a)(1), without the details of the invention being disclosed to the public.

Supply agreements, licensing discussions, and development contracts involving the patented subject matter can therefore start the clock even when the parties have agreed to keep the terms confidential. A non-disclosure agreement prevents a counterparty from revealing information; it does not neutralize the commercial nature of the transaction for purposes of the on-sale bar.

AIA vs. pre-AIA: geographic scope

The AIA significantly expanded the geographic reach of the on-sale bar. Under the AIA, the on-sale bar applies without geographic restriction, covering sales and offers for sale anywhere in the world. An offer made to a buyer in another country is equally capable of triggering the bar as one made domestically.

Under pre-AIA 35 U.S.C. § 102(b), the on-sale bar was limited to sales or offers for sale occurring in the United States. A sale where both manufacture and delivery occurred in a foreign country did not directly trigger the pre-AIA on-sale bar. Applications with effective filing dates that predate the AIA transition are analyzed under the pre-AIA geographic limitation, while AIA applications face the worldwide scope.

Grace period exception

The AIA provides a grace period exception that can shelter the inventor from the bar. Under 35 U.S.C. § 102(b)(1)(A), a disclosure (including a sale or offer for sale) made by the inventor or joint inventor, or by another who obtained the subject matter directly or indirectly from the inventor, within the statutory period before the effective filing date is excepted and does not constitute prior art.

The exception has important limits:

• Traceability is required. The grace period exception does not extend to an independent third-party sale; it applies only when the disclosure is traceable to the inventor as the original source of the subject matter.
• The window is fixed. Sales occurring before the statutory window closes are not excepted, regardless of the inventor's involvement. Verify the applicable window against the current statute before advising a client.
• Pre-AIA operated differently. The AIA grace period is not identical in structure to the pre-AIA safe harbor. Do not assume the same analysis applies across both regimes.

Experimental use exception

Not every sale between an inventor and a third party triggers the bar. A sale or offer for sale made primarily for experimental purposes does not invoke the on-sale bar: experimentation must be the primary purpose and any commercial exploitation must be incidental.

Courts assess objective evidence when evaluating this exception, not an inventor's subjective state of mind. An inventor's secretly held intent to experiment is unavailing without objective evidence of that purpose. Relevant objective factors include whether the inventor retained control over the activity, whether a secrecy obligation was imposed on the counterparty, whether the inventor kept experimental records, whether the inventor monitored the activity to evaluate the invention's function, and whether any payment was made.

Practical notes for practitioners

• Audit commercial activity before drafting claims. Any offer, agreement, or negotiation involving the subject matter of the invention should be identified and dated early in prosecution. The bar can arise from a term sheet, supply agreement, or development contract if both Pfaff prongs are met.
• Confidentiality agreements do not solve the on-sale problem. After Helsinn, a non-disclosure clause keeps terms private but does not prevent the underlying sale from constituting prior art. "Just add an NDA" is not adequate legal advice for this risk.
• Verify geographic scope against the applicable law. For applications governed by pre-AIA § 102(b), a purely foreign transaction may not trigger the bar. For AIA applications, there is no geographic savings.
• The grace period requires inventor-originated activity. Establish clearly whether the commercial activity traces back to the inventor. A third-party sale not derived from the inventor is not protected by the grace period even if the subject matter is the same.
• Build a contemporaneous experimental use record. If the experimental use exception is at issue, gather the test protocols, inventor monitoring logs, any secrecy conditions imposed on the counterparty, and evidence that no revenue was generated. After-the-fact characterization of a sale as experimental is difficult to sustain without contemporaneous documentation.
• Private does not mean non-barring. A one-on-one offer made in a private meeting, never publicly announced, can still be a commercial offer for sale if it contains binding material terms and the invention was ready for patenting.