A unilateral contract is an agreement in which one party (the offeror) makes a promise that will be fulfilled only if another party (the offeree) performs a requested act. The offeree is not obligated to act, but if they do complete the act according to the offer’s terms the offeror becomes legally bound to pay or perform. Typical real‑world examples include reward offers, task‑for‑payment arrangements (e.g., pay someone to mow your lawn), and many insurance promises where payment is triggered by a covered event.
Key takeaways
– A unilateral contract binds only the offeror until and unless the offeree completes the specified performance.
– The offeree can accept only by performing the requested act; there is generally no contractual duty to begin performance.
– Modern contract doctrine often protects an offeree’s reliance: once performance has begun, the offer may become non‑revocable to the extent of that performance.
– Disputes often hinge on whether the offer’s terms were sufficiently certain and whether the offeree actually completed the required act.
Understanding unilateral contracts
Unilateral contracts contrast with bilateral contracts. In a bilateral contract both parties exchange promises (I promise to do X if you promise to do Y). In a unilateral contract, the offeror promises something in return for an act, not for a promise. Common situations:
– Rewards: “$5,000 for information leading to the arrest of X.”
– Task offers: “I’ll pay $200 if you paint my garage.”
– Insurance-like promises: The insurer promises to pay benefits if a specified event occurs (though insurance contracts have aspects of both unilateral and bilateral contracts because insureds pay premiums).
Types and examples
– Open requests/rewards: public offer for information or action (police rewards; “lost dog” posters).
– Casual service offers: one‑off service-for-payment (yard work, house painting).
– Insurance commitments: insurer’s obligation to pay when a covered loss occurs (often governed by statute and policy terms).
The four elements required for enforceability
For a unilateral contract to be enforceable under general contract principles, the familiar elements must be present
1. Offer (Agreement)
– A clear, definite offer must be made: the offeror must identify what performance will trigger payment and the amount/timing of payment.
2. Consideration
– There must be consideration (something of legal value). The offeree’s performance generally supplies the consideration for the offeror’s promise.
3. Intention to create legal relations
– The parties must intend the promise to be legally binding (not just an informal invitation).
4. Certainty (Definite terms)
– The terms—what must be done, by when, by whom, and how payment will be made—must be sufficiently certain to be enforced.
How to know whether an offer is unilateral
Ask:
– Does acceptance require a promise, or performance? If only performance accepts the offer, it’s unilateral.
– Are the promised obligations one‑sided until completion? If yes, unilateral.
– Are terms clear about the performance required and the reward/payment? If not, courts may treat it as too vague.
Practical steps — for offerors (how to make a solid unilateral offer)
1. Put the offer in writing and clearly label it an “offer” with exact terms:
• Describe the required performance in detail.
• Specify the payment amount or reward and how and when it will be paid.
• State any deadlines and any proof you require to support a claim.
2. Identify who may accept (single person, any person, a class of people).
3. State whether you intend the offer to be revocable and under what conditions; if you want irrevocability while performance is underway, include language granting an “option” once performance begins or specify how performance must be commenced.
4. Provide contact or payment procedures and how to submit evidence of performance.
5. Preserve records of the offer (advertisement, e‑mail, dated social posts) to avoid disputes later.
Practical steps — for offerees (how to accept and protect your rights)
1. Read the offer carefully; confirm the exact actions required and any deadlines.
2. If possible, begin performance in a way that can be documented (photos, timestamps, witnesses, receipts).
3. Preserve evidence of your performance: video, photos, signed witness statements, emails, bank transfers for expenses, GPS logs where relevant.
4. If the offer requires notice of completion, provide the notice promptly in the required manner.
5. If the offeror refuses payment after you’ve completed the terms, collect documentation and consider sending a demand letter; small‑claims court is common for many reward disputes.
Revocation and partial performance
– Generally, the offeror may revoke a unilateral offer any time before the offeree begins performance. However, many courts recognize that once the offeree has begun performance (or reasonably relied on the offer), the offer may become irrevocable to the extent necessary to allow the offeree to complete performance (see Restatement (Second) of Contracts §45—part performance creates an option contract).
– If performance is only partially completed and then abandoned, the offeror usually owes nothing, unless the offeree is entitled to reliance damages or part‑performance compensation under equitable doctrines.
Breach and remedies
– If the offeree completes performance and the offeror refuses to pay, the offeree can sue for breach of contract and seek the promised amount.
– If the offeror revokes before performance begins, the offeree generally has no breach claim unless there was an enforceable option or promissory estoppel due to reliance.
– Where a mistake affects the terms, courts may reform the contract, rescind it, or deny enforcement depending on whether the mistake was mutual and its effect on terms.
Are mistakes enforceable?
– Mutual mistakes that go to the core of what was agreed may make a contract voidable.
– If one party made a unilateral mistake and the other party did not know, courts are less likely to cancel the contract, unless enforcing it would be unconscionable.
– In reward/unilateral contexts, proof and clarity reduce mistakes: specify required proof and performance standards.
Checklist before relying on or issuing a unilateral contract
– Are the terms sufficiently specific? (what, how, when, how paid)
– Is there written evidence of the offer?
– Do you understand whether starting performance will secure irrevocability?
– Can you document completion in a way that will convince a court or other decision‑maker?
– Have you considered consumer protection, insurance, tax, or regulatory implications?
Bottom line
Unilateral contracts are practical tools for offers payable only upon completed performance (rewards, discrete tasks, certain insurance triggers). They are enforceable when the offer is clear, supported by consideration, and intended to create legal relations. To avoid disputes: draft clear terms, require and provide methods for proof, preserve records, and understand the limited circumstances in which an offeror may revoke once performance has begun.
Source
– Investopedia, “Unilateral Contract”:
– Restatement (Second) of Contracts §45 (part performance and option contracts) — for doctrinal context (U.S.).