In Carlill v. Carbolic Smoke Ball Co. (1893), the English Court of Appeal held that a company's advertisement promising £100 to anyone who used its product as directed and still caught influenza was a binding unilateral contract, not a mere puff or invitation to treat. Because the company deposited £1,000 in a bank to show its sincerity, the promise was a genuine offer the public could accept by performing the requested conditions—using the smoke ball as directed. Mrs. Carlill accepted by performance and did not need to notify the company beforehand, so she was entitled to the £100.

This is one of the very first cases you'll read in Contracts, and there's a reason it sticks around: it's the cleanest illustration ever written of the difference between an offer and an ad, between a bilateral and a unilateral contract, and between a promise the law enforces and marketing hot air. Almost every element of a contract shows up in one weird story about a quack flu remedy. Learn it cold—your professor will circle back to it for the rest of the semester.

What is the case summary for Carlill v. Carbolic Smoke Ball Co.?

Carlill v. Carbolic Smoke Ball Co., [1893] 1 Q.B. 256, was decided by the English Court of Appeal in 1893. The Carbolic Smoke Ball Company advertised that it would pay £100 to any person who used its smoke ball three times daily for two weeks and still contracted influenza; it also stated it had deposited £1,000 with the Alliance Bank to show its sincerity. Louisa Carlill bought and used the ball as directed, caught the flu anyway, and sued for the £100. The court unanimously held that the advertisement constituted a binding unilateral offer, that Mrs. Carlill had accepted it by performance, and that she was entitled to recover.

What are the key facts of Carlill v. Carbolic Smoke Ball Co.?

Only a handful of facts do the real work here—know these:

• The Carbolic Smoke Ball Company sold a device (a rubber ball filled with carbolic acid) that users inhaled to prevent influenza and other ailments.
• The company placed a newspaper advertisement promising to pay £100 to anyone who used the ball three times daily for two weeks according to the directions and still caught influenza.
• The ad stated the company had deposited £1,000 with the Alliance Bank "showing our sincerity in the matter."
• Louisa Carlill saw the advertisement, purchased a smoke ball, and used it as directed from mid-November 1891 until she contracted influenza in January 1892.
• She claimed the £100. The company refused, and she sued.

That £1,000 deposit is not throwaway color—it's the fact that sinks the company's best defense. Underline it.

What was the procedural history?

Mrs. Carlill brought her claim in the Queen's Bench Division, where Justice Hawkins ruled in her favor. The Carbolic Smoke Ball Company appealed to the Court of Appeal, which affirmed the judgment for Mrs. Carlill. The lead opinions were delivered by Lord Justices Lindley, Bowen, and A.L. Smith.

What was the legal issue in Carlill v. Carbolic Smoke Ball Co.?

The core issue: Was the company's advertisement a legally binding offer that Mrs. Carlill could accept by performance, thereby forming an enforceable contract entitling her to the £100? Wrapped inside that are several sub-issues the company raised as defenses—whether the ad was mere "puff," whether it was too vague to be a contract, whether acceptance had to be communicated, and whether Mrs. Carlill gave any consideration.

What did the court hold and what is the rule?

Holding: The Court of Appeal held that the advertisement was a binding unilateral offer to the world, that Mrs. Carlill accepted it by performing the specified conditions, and that she was therefore entitled to the £100.

The rules that go in your outline:

• A general offer to the world can be a valid offer. An offer need not be made to a specific person; it can be made to anyone who performs the stated conditions, and a contract forms with each person who does.
• A unilateral contract is accepted by performance, not by a return promise. When an offer requests an act in exchange for a promise, performing that act is the acceptance.
• Notification of acceptance is not required before performance where the offer, expressly or by its nature, dispenses with it. By requesting performance, the offeror impliedly waives the need for prior communication of acceptance.
• Performing an inconvenient act at the offeror's request is valid consideration. Using the ball as directed was a detriment/inconvenience to Mrs. Carlill; the company also obtained a benefit (increased sales). Either satisfies consideration.
• Objective intent controls. Whether an advertisement is a binding offer or mere puffery is judged by how a reasonable person would read its words—here, the specific promise plus the £1,000 deposit signaled genuine intent to be bound.

What was the court's reasoning?

The company threw every defense it had at the wall. The Court of Appeal knocked them down one by one, and the way it did so is the meat of the case.

"It was just an advertising puff." Lord Justice Bowen answered that the ad wasn't vague marketing bluster because it named a specific sum and, crucially, referred to the £1,000 deposited with the bank to "show sincerity." A reasonable reader would understand this as a serious promise, not hyperbole. The objective meaning of the words, not the company's private intent, controlled.

"You can't make an offer to the whole world." The court held that an offer can indeed be made to the world at large. It ripens into a contract only with the specific people who come forward and perform the conditions—so there is no problem of contracting with millions. Bowen L.J. analogized to a reward offered for a lost dog: anyone who finds and returns it can claim.

"The terms are too vague." The court read the ad on its ordinary terms—use as directed, for the relevant period—and found the conditions determinate enough to enforce.

strong>"Mrs. Carlill never notified us she accepted." Lord Justice Lindley explained that in this kind of offer, the offeror requests performance of the conditions and, by doing so, dispenses with the need for prior notice of acceptance. Performance of the conditions is itself the acceptance. (In an ordinary bilateral contract, acceptance must be communicated; a unilateral offer that invites performance impliedly waives that.)

"There was no consideration." The court found consideration two ways. Mrs. Carlill suffered a detriment/inconvenience by using the ball three times a day for weeks at the company's request. And the company received a benefit in the form of increased sales flowing from the promotional promise. Under classic bargain theory, a detriment incurred at the promisor's request supplies consideration.

Why does Carlill v. Carbolic Smoke Ball Co. matter?

Carlill is the anchor case for the unilateral contract and the doctrine that advertisements are generally invitations to treat—unless the language makes them offers. It sits early in almost every Contracts course, in the offer-and-acceptance unit, and it neatly packages nearly the entire skeleton of contract formation: intent to be bound (objective theory), offer vs. invitation to treat, acceptance by performance, communication of acceptance, and consideration. When your professor later teaches Lefkowitz v. Great Minneapolis Surplus Store (the "first come, first served" fur ad case), the reward cases, or the modern rule that ads are usually not offers, they're building on the framework Carlill sets up. It's a case you keep in your back pocket all semester.

Cold-call prep: what will the professor ask?

Carlill is a classic Socratic warm-up because it's rich but not technical. Expect these:

"Why isn't this just an advertisement—why is it an offer?" Because a reasonable reader would take it as a serious promise, given the specific £100 sum and the £1,000 bank deposit expressly stated to show sincerity. Objective intent, judged from the words, controls—and these words show intent to be bound. Contrast the general rule that ads are invitations to treat.

"How can you make a contract with the whole world?" You don't contract with everyone at once. The offer to the world becomes a binding contract only with each individual who performs the conditions. Use Bowen L.J.'s reward analogy.

"Did Mrs. Carlill have to tell the company she was accepting?" No. In a unilateral contract, the offeror requests performance and thereby waives the need for prior notice of acceptance. Performing the requested act is the acceptance. Be ready to contrast this with bilateral contracts, where acceptance must be communicated.

"What was the consideration?" Two answers: the detriment/inconvenience to Mrs. Carlill in using the ball as directed, and the benefit to the company in increased sales. Either supports the promise.

"Is this a bilateral or unilateral contract? How do you know?" Unilateral. The company sought an act (using the ball and still getting sick), not a return promise. Acceptance came by performance.

The trap question—"So is every advertisement an offer now?" No, and don't get flustered. The default rule is that ads are invitations to treat, not offers. Carlill is the exception that proves the rule: it became an offer because its specific language and the deposit showed genuine intent to be bound. Say the default first, then explain why this ad was different.

How does Carlill show up on the exam?

Carlill's doctrine surfaces on issue-spotters as a formation problem dressed up as a promotional promise: a store or manufacturer runs an ad or a "$X if our product fails" guarantee, and a customer performs and demands payment. Your job is to run the offer analysis. First ask whether the language is a genuine offer or mere puff—look for a specific promise, a specific sum, and any signal of serious intent (the fact that mirrors the £1,000 deposit). Then classify it as unilateral (accepted by performance) versus bilateral. If unilateral, note that notification of acceptance generally isn't required before performance. Finally, run consideration—identify the detriment the performer incurred at the promisor's request.

The trap students fall into: reflexively writing "advertisements are not offers, so no contract" and stopping there. That earns you almost nothing. The whole point of Carlill is that the general rule has an exception when the language and surrounding facts show intent to be bound. The professor plants an ad specifically to see whether you spot the Carlill exception. Always state the default rule and then analyze whether the specific facts push it into offer territory.

What related cases are taught alongside Carlill?

• Lefkowitz v. Great Minneapolis Surplus Store (1957) — the "first come, first served" fur-stole ad; the American counterpart holding that a sufficiently definite ad can be an offer.
• Leonard v. Pepsico (1999) — the Harrier Jet commercial; the court held it was obviously a joke/puff, the modern flip side of Carlill on objective intent and whether an ad is a serious offer.
• Lucy v. Zehmer (1954) — the objective theory of intent (the napkin sale of a farm), often paired to reinforce that intent is judged objectively.
• Reward and "lost dog" cases generally — classic examples of general offers accepted by performance.

Frequently asked questions

See the FAQ section below for the questions students ask most about Carlill.