On-sale bar
An invention that was the subject of a commercial offer for sale more than one year before the effective filing date of a patent application is barred from patenting. Under Pfaff, the bar applies only when the invention was both the subject of a commercial offer and ready for patenting at the critical date. Under Helsinn, the AIA carried that rule forward — and continues to reach secret and confidential sales.
The rule
A patent claim is invalid under 35 U.S.C. § 102(a)(1) if the claimed invention was "on sale" before the effective filing date of the application. Section 102(b)(1) provides a one-year grace period for the inventor's own pre-filing disclosures and sales. The "critical date" for the on-sale analysis is therefore one year before the effective filing date.
The Supreme Court's two-prong test from Pfaff v. Wells Electronics, Inc., 525 U.S. 55 (1998), governs: the bar applies if (1) the invention was the subject of a commercial offer for sale, and (2) the invention was ready for patenting. Id. at 67. Each element must be present at the critical date for the bar to apply.
The AIA preserved the on-sale bar with the same statutory phrasing — "on sale" — and the Court in Helsinn Healthcare S.A. v. Teva Pharmaceuticals USA, Inc., 586 U.S. 123 (2019), confirmed that the AIA's on-sale bar covers commercial sales even where the sale's existence or the details of the invention are kept confidential. The pre-AIA "secret sale" caselaw therefore continues to operate under the AIA.
Statutory and constitutional source
The on-sale bar is statutory. The pre-AIA version, 35 U.S.C. § 102(b) (2006), barred patents where the invention was "in public use or on sale in this country, more than one year prior to the date of the application." The AIA replaced this with 35 U.S.C. § 102(a)(1), which bars patents where the invention was "in public use, on sale, or otherwise available to the public before the effective filing date."
Two changes are textually significant. First, the AIA's "or otherwise available to the public" catchall raised a question whether the term "on sale" must now itself mean a publicly known sale. The Court in Helsinn answered no. 586 U.S. at 132. The pre-AIA understanding — that secret commercial activity could trigger the bar — was carried forward.
Second, the AIA dropped the geographic limitation "in this country." Foreign sales now count. This conforms § 102(a)(1) to international practice and aligns the on-sale bar with the AIA's worldwide approach to anticipation.
The constitutional foundation lies in the Patent and Copyright Clause's "limited Times" requirement, U.S. Const. art. I, § 8, cl. 8. The on-sale bar, like the public use bar, prevents inventors from extending the patent monopoly by commercializing an invention before filing. Pennock v. Dialogue, 27 U.S. (2 Pet.) 1 (1829).
The framework the courts apply
Prong one: commercial offer for sale
Whether a transaction is a commercial offer for sale is a question of federal patent law informed by general contract principles. Group One, Ltd. v. Hallmark Cards, Inc., 254 F.3d 1041 (Fed. Cir. 2001). An offer for sale must be sufficiently definite that another party could make it into a binding contract by simple acceptance. Mere advertisements, price lists, or expressions of interest do not satisfy the prong; a specific offer reciting price, quantity, and terms generally does.
Both completed sales and unaccepted offers can trigger the bar. The bar covers sales by the inventor, by the assignee, and — in pre-AIA law — by third parties who placed the invention on sale. Under § 102(a)(1) post-AIA, third-party on-sale activity also can bar a later patent (subject to the inventor's grace period and § 102(b)(2) exceptions for derived disclosures).
A "stocking" or "supply" agreement covering inventory of a commercial product can be an on-sale event, even if the product is not delivered until after the critical date. Helsinn, 586 U.S. at 127–28 (Helsinn's supply and purchase agreements with MGI Pharma, executed before the critical date and disclosed to the public though their financial terms were redacted, qualified as a sale).
Prong two: ready for patenting
The invention must be ready for patenting at the critical date. Pfaff, 525 U.S. at 67. Ready for patenting can be shown in either of two ways: (1) reduction to practice, or (2) drawings or other descriptions sufficiently specific to enable a person of ordinary skill in the art to practice the invention. Id.
Reduction to practice requires construction of an embodiment that meets every limitation and a determination that the invention works for its intended purpose. The "works for its intended purpose" requirement varies by technology — for simple mechanical inventions, mere construction may suffice; for chemical or pharmaceutical inventions, demonstrated efficacy is often required.
The Federal Circuit has held that the second route — sufficient drawings or descriptions — can be satisfied by a complete written specification or detailed engineering drawings, even without a working prototype. Robotic Vision Systems, Inc. v. View Engineering, Inc., 249 F.3d 1307 (Fed. Cir. 2001).
Experimental use exception
The on-sale bar does not apply to bona fide experimental use. City of Elizabeth v. Pavement Co., 97 U.S. 126 (1877), held that an inventor's six-year public testing of wooden-block paving on a Boston toll road was experimental and did not trigger the on-sale or public-use bars. The Court emphasized that experimental use is "the use of [the invention] by the inventor himself, or of any other person under his direction, by way of experiment, and in order to bring the invention to perfection." Id. at 134.
The exception is narrow. Sales conducted primarily for commercial gain are not experimental, even if the inventor is also gathering performance data. EZ Dock, Inc. v. Schafer Systems, Inc., 276 F.3d 1347 (Fed. Cir. 2002). Factors include the necessity of public testing to perfect the invention, who controlled the testing, whether the inventor monitored the use, the duration of the testing, whether payment was made, and whether confidentiality was required.
After Pfaff and Helsinn, the experimental-use exception remains available but operates effectively as a defense to the "commercial offer" prong: an offer that is genuinely experimental rather than commercial does not trigger the bar.
Burden and proof
The on-sale bar must be proved by clear and convincing evidence. Microsoft Corp. v. i4i Limited Partnership, 564 U.S. 91 (2011) (clear-and-convincing standard for invalidity defenses generally). The accused infringer carries the initial burden of identifying a pre-critical-date offer or sale and showing readiness for patenting. The patentee may then rebut by showing the activity was experimental, that no offer was made, or that the invention was not ready for patenting.
Both prongs of Pfaff are mixed questions of law and fact. The legal question of whether a particular communication is a "commercial offer for sale" is reviewed de novo, while the underlying factual findings are reviewed for clear error or substantial evidence. Group One, 254 F.3d at 1045–46.
The on-sale bar is regularly litigated on summary judgment when the prosecution and corporate record contains a clear pre-critical-date contract. It can also be raised in post-grant review at the PTAB during the first nine months after issuance — though it cannot be raised in inter partes review, which is limited to anticipation and obviousness over patents and printed publications.
Interaction with related doctrines
The on-sale bar is one of two principal pre-filing bars in § 102(a)(1); its companion is the public use bar. The two often overlap factually: a commercial demonstration may be both a public use and an on-sale event. They are distinct doctrines with overlapping experimental-use exceptions.
Conceptually, the on-sale bar is a species of anticipation: the pre-critical-date sale acts as an anticipating reference. Many of the same construction principles apply, including the rule that the prior reference must disclose every limitation as arranged in the claim. But the on-sale bar differs because the prior reference is the inventor's (or another party's) commercial activity rather than a printed publication.
The on-sale bar does not require that the on-sale embodiment have been reduced to practice in a manner that would also satisfy written description and enablement; the Pfaff "ready for patenting" prong is somewhat lower. But where a sale is offered in the alternative as anticipating prior art, the disclosure must satisfy traditional anticipation requirements.
The bar also interacts with the doctrine of inequitable conduct: failure to disclose a material on-sale event during prosecution can give rise to an unenforceability defense if both the materiality and intent prongs of Therasense are met. The on-sale event must be but-for material — that is, the patent would not have issued had the examiner known of it.
Practical notes
For inventors and counsel, the critical-date analysis is often the first task on docketing. The conservative practice is to file a U.S. application — typically a provisional under 35 U.S.C. § 111(b) — before any commercial offer for sale, even an offer subject to a non-disclosure agreement. Helsinn ended any safe harbor for confidential commercial activity, and the marginal cost of an early provisional is small.
Stocking, manufacturing, and licensing agreements deserve particular attention. A supply agreement that is itself secret but whose existence is publicly announced (as in Helsinn) is sufficient to trigger the bar. Even a wholly confidential agreement may trigger the bar; the Court in Helsinn declined to disturb the Federal Circuit's longstanding view that secret sales bar patents. 586 U.S. at 132–33.
For startup-company prosecution, beware investor demonstrations. A demonstration coupled with a term sheet, a price proposal, or an option to purchase can constitute a commercial offer. Conversely, a demonstration under a true non-disclosure agreement, with no price discussion and no offer of supply, generally does not trigger the bar (though may pose public-use risk).
For litigation, on-sale-bar discovery focuses on the patentee's pre-critical-date corporate documents: contracts, board minutes, marketing materials, regulatory filings, and (in pharmaceutical cases) FDA submissions. SEC filings often disclose supply agreements without disclosing the technical details of the underlying invention; under Helsinn, that combination still triggers the bar.
Pharmaceutical patentees should be especially attentive to pre-NDA supply and licensing agreements with marketing partners. Hatch-Waxman litigation under 21 U.S.C. § 355(j) and 35 U.S.C. § 271(e)(2) frequently turns on whether a pre-critical-date supply agreement triggered the on-sale bar.
Open questions
The full reach of Helsinn remains to be tested. The Court emphasized that the supply agreement at issue was disclosed publicly, even if its technical details were not, and reserved judgment on whether a wholly confidential commercial transaction — for example, an internal supply arrangement among related entities — would suffice. The Federal Circuit has continued to apply the "secret sale" rule under both the pre-AIA and AIA statutes, but the precise outer boundary is unsettled.
The treatment of foreign sales under post-AIA § 102(a)(1) is also in development. The text plainly drops the "in this country" limitation, and some district courts have applied the bar to foreign offers and sales. But proof issues — including how to establish the existence and timing of foreign transactions, and how to translate foreign legal concepts of offer and acceptance — remain practical hurdles.
Finally, the experimental-use exception's continued vitality after the AIA is unsettled in form, though courts have continued to apply it in substance. The exception was historically a judicial gloss on the pre-AIA "on sale" language, and the AIA carries the same language forward; courts have therefore continued to apply City of Elizabeth's framework, but no Supreme Court or en banc Federal Circuit decision has formally re-affirmed it under the AIA.
See also
- Public use barThe companion §102(a)(1) bar; on-sale and public-use events frequently overlap on the facts.
- AnticipationThe broader §102 doctrine of which the on-sale bar is a species.
- ObviousnessA pre-critical-date sale of a similar product can also serve as a §103 reference.
- Inequitable conductConcealment of a material pre-critical-date sale can support an inequitable-conduct defense.
- Written description and enablementDistinct from the "ready for patenting" prong, but factually related.
- Post-grant reviewPTAB venue in which on-sale-bar challenges may be raised within nine months of issuance.
- Inter partes reviewCannot adjudicate the on-sale bar; limited to printed-publication and patent prior art.
- Title 35 referenceStatutory text of §§102, 111, and related provisions.
- GlossaryDefinitions of "critical date," "ready for patenting," and "experimental use."
Last reviewed: 2026