Unilateral Contracts Explained: Australian Business Essentials

When you’re running a business in Australia, you’ll deal with contracts every day - from customer offers to staff incentives and promotional campaigns. Among the different types of agreements you might use, “unilateral contracts” come up more often than you’d expect, and understanding how they work can help you avoid disputes and set clear expectations from the start.

In this guide, we break down unilateral contracts in plain English, explain how they differ from other contracts, clear up common myths (including how revocation works), and share practical examples you can use in your business. We’ll also cover key risks to watch for and the documents that help make your offers clear and enforceable.

What Is A Unilateral Contract In Australia?

A unilateral contract is an agreement where one party makes a promise that can only be accepted by someone performing a specified act. In other words, the promisor is only obliged to perform once the other side actually does the thing requested (rather than promising to do it).

Classic example: “$500 reward for the return of my lost dog.” You’re not asking for a promise - you’re offering to pay if someone carries out a specific act. The person who returns the dog accepts your offer by performance, not by saying “I agree.”

As with any contract in Australia, the usual elements must be present for a unilateral contract to be binding:

• Offer: A clear promise (“We’ll pay X if you do Y”).
• Acceptance: Occurs through the required act being performed.
• Consideration: The act itself is the value exchanged for the promise.
• Intention: In business contexts, it’s generally presumed you intend legal relations.
• Certainty: Terms need to be sufficiently clear to be enforceable.

One often-overlooked requirement is knowledge of the offer. To accept by performing, the person must know about the offer when doing the act. If someone performs the act without knowing the offer exists, there’s generally no acceptance and therefore no contract (this point has been emphasised in Australian case law).

If you want a refresher on the fundamentals, it’s worth revisiting how offer and acceptance operate under Australian contract law.

Unilateral Vs Bilateral Contracts: What’s The Difference?

Most business contracts are “bilateral” - both sides exchange promises and are bound once they agree. For instance, a supplier promises to deliver stock and the buyer promises to pay. Everyone is on the hook from the moment of agreement.

Unilateral Contracts (In Practice)

• One party promises to do something if someone else performs a specific act.
• There’s no obligation on anyone to act - but if they do, the promise must be honoured.
• Acceptance happens by performance, not by a return promise.

Bilateral Contracts (In Practice)

• Each party makes a promise to the other (e.g. deliver and pay).
• Both are bound once the promises are exchanged.
• Acceptance is typically by agreeing to the terms.

The distinction matters for timing, risk and enforcement. In unilateral situations, the key question is often: exactly what action counts as acceptance - and when does your obligation to perform kick in?

How Do Unilateral Offers, Acceptance And Revocation Work?

This is where many businesses get tripped up. Let’s unpack three practical points: making the offer, accepting by performance, and revoking the offer.

Making The Offer

To create a unilateral offer, your promise must be clear and sufficiently specific. If you say “We might pay a reward for helpful information - details to be decided,” that’s probably too vague to enforce. Set out the action required, any eligibility conditions, and limits like timeframes or caps.

Acceptance By Performance (And Knowledge Of The Offer)

In unilateral contracts, acceptance happens when the offeree performs the required act. However, the person must know about the offer when they perform. If they had no knowledge of your offer when acting, in most cases there won’t be a binding contract because there was no acceptance in the legal sense.

Can You Revoke A Unilateral Offer?

Generally, a unilateral offer can be withdrawn at any time before acceptance. But in practice, the timing and manner of revocation matters.

Australian courts have cautioned against a blanket rule that “starting performance automatically makes the offer irrevocable.” Instead, whether you can revoke after someone begins performance depends on the wording of your offer and the surrounding circumstances. In some cases, an implied obligation not to revoke may arise once the offeree has embarked on performance in reliance on your offer - but this isn’t automatic and is assessed case by case.

Practical takeaway: if you’re running a promotion or reward, be explicit about how and when the offer can end, and how acceptance works. Clear drafting reduces the risk of disputes about revocation or partial performance.

Where Do Unilateral Contracts Show Up In Business?

You may already be using unilateral contracts without labelling them as such. Here are common scenarios.

Public Rewards

“$1,000 for information leading to recovery of stolen equipment.” This is a textbook unilateral offer. Acceptance occurs when someone, knowing about the offer, does the thing requested.

Referral And Promotion Programs

“Get a $100 credit if you refer a friend who becomes a paying customer.” The credit only arises if a specified event occurs. Your terms should define what counts as a “referral,” any exclusions, and how and when credits are applied. Publishing those terms on your site sits neatly in your Website Terms and Conditions.

Sales Or Performance Bonuses

“An extra bonus if you exceed $50,000 in quarterly sales.” If framed as a public promise contingent on performance, this can operate unilaterally. If it’s part of an employment package, it may be better handled in a written Employment Contract or bonus policy to avoid arguments about thresholds, dates and what counts toward the target.

Service Guarantees

“If we don’t respond within 24 hours, your next service is free.” The customer only gets the benefit if a condition occurs. Make sure the guarantee sits comfortably with your Australian Consumer Law (ACL) obligations and is drafted precisely so it’s clear when it applies.

Note: Insurance policies are usually bilateral (you pay premiums; the insurer promises cover on agreed terms). While the payout depends on an event occurring, the policy itself is typically formed by mutual promises, not by acceptance via performance.

Legal Risks And How To Manage Them

Unilateral offers are powerful tools for engagement and incentives - but they do carry legal risks. Here’s how to stay on the right side of the law and reduce disputes.

1) Clarity And Certainty

Ambiguous offers are the fastest route to a dispute. Spell out:

• Exactly what action qualifies (and who is eligible).
• Any limits (timeframes, quantity caps, geographic limits, “first come, first served”).
• How to claim or verify performance.

Publishing clear rules in your customer terms or a promotion-specific page helps. If you’re running a giveaway or “refer-a-friend” incentive, formal Competition Terms & Conditions keep things consistent and easier to enforce.

2) Knowledge Of The Offer

If someone completes the act without knowing your offer existed, there’s usually no acceptance. Make sure your offer is actually communicated to the audience you want to reach (and keep records of how and when you published it).

3) Revocation And Timing

Be upfront about when the offer ends and how revocation will be communicated. Avoid a situation where someone has reasonably relied on your offer and you attempt to cancel mid-stream. That’s where courts may imply obligations or look to doctrines like estoppel, depending on the facts.

4) Australian Consumer Law (ACL)

Your public offers and promotions must not mislead. Section 18 of the ACL prohibits misleading or deceptive conduct in trade or commerce. Claims must be accurate, conditions should be prominent, and any limitations must be clearly disclosed - not buried in fine print. If you’re unsure about the line between enthusiastic marketing and risk, revisit the core rule in section 18 of the ACL.

5) Privacy And Data

Referral programs and promotions often involve collecting names, emails and other personal information. If you collect personal data, you’ll generally need a clear Privacy Policy and processes to handle that information lawfully.

6) Internal Alignment

Make sure your team knows exactly how the offer works, what to say to customers, and how to verify claims. Inconsistent messaging is a frequent source of complaints.

Documents That Support Clear Unilateral Offers

Even though unilateral contracts can arise from a simple public promise, you’ll minimise risk by putting the rules in writing and housing them in the right place. Most businesses use a mix of the following documents.

• Website Terms and Conditions: The logical home for general customer-facing rules, including how promotions are run, eligibility, and how credits or rewards are applied. See Website Terms and Conditions.
• Competition Terms & Conditions: If you’re running competitions, games of chance or public reward schemes, a dedicated set of rules manages entry, verification, winner selection and prize fulfilment. Use formal Competition Terms & Conditions for each campaign.
• Employment Contract or Bonus Policy: If you’re offering performance bonuses to staff, documenting the criteria, measurement periods and payout rules in an Employment Contract or policy avoids confusion and sets expectations early.
• Customer Terms (Service or Sale): If you supply services or goods, your customer contract can set baseline terms and reference any guarantees or promotional promises to keep everything consistent.
• Privacy Policy: If you collect personal information (e.g. in a referral or loyalty program), your Privacy Policy should explain what you collect, why, and how it’s used.

If you’re an online platform, you may also need app or platform terms to deal with user behaviour, credits, and reward mechanics. Your public promises should align with those rules so there’s no contradiction.

Mistakes, Misleading Conduct And Disputes: What Happens Next?

Despite best efforts, disagreements can happen. Here’s how Australian law typically treats common issues in the unilateral contract space.

Unilateral Mistake

A unilateral mistake is where one party is mistaken about a fundamental term, but the other party is not. In Australia, a contract won’t usually be set aside just because one party made an error. However, if the other party knew or ought reasonably to have known about the mistake and proceeded anyway, a court may intervene (for example, on the basis of unconscionability or by granting equitable relief). Each case turns on its facts.

Misleading Or Deceptive Conduct

If the dispute stems from unclear or exaggerated claims in your offer, the ACL may apply. Businesses must avoid conduct that misleads consumers - whether by what you say, how you say it, or what you fail to disclose. If a promotion is likely to mislead, it can be unlawful even if you didn’t intend to mislead. It’s best to sanity-check the wording of your promotions and ensure they reflect reality. Where the issue relates to false statements, consider the law on misrepresentation as well.

Knowledge Of The Offer (Acceptance Problem)

If a claimant didn’t know about the offer when performing the act, they’ll usually have difficulty establishing acceptance. Good record-keeping around how and when you communicated the offer (e.g. website screenshots, social posts, email blasts) helps resolve this quickly.

Revocation And Reliance

If the dispute is about whether you could revoke the offer after someone started performing, the outcome depends on the wording of the offer and the overall circumstances. Australian courts have indicated that starting performance does not automatically make an offer irrevocable. That said, an implied obligation not to revoke can arise depending on construction and reliance. To avoid this scenario, state clearly when the offer ends and how you will communicate any changes or withdrawals.

How Disputes Are Resolved

Many issues can be solved informally by applying the written terms and the evidence of performance. Where that’s not possible, consider negotiation, mediation or formal legal steps. Prevention is best: clear terms, consistent communications and sound record-keeping are your strongest protection.

Key Takeaways

• A unilateral contract is a promise that can only be accepted by performance - the other party isn’t bound to act, but if they do, you must keep your promise.
• Acceptance requires knowledge of the offer at the time of performance; without it, there’s usually no contract.
• Starting performance doesn’t automatically make a unilateral offer irrevocable in Australia - revocation and reliance are assessed case by case and depend on the wording and circumstances.
• Use precise, accessible terms and publish them in the right place (for example, your Website Terms and Conditions and Competition Terms & Conditions).
• Promotions must comply with the Australian Consumer Law - avoid misleading claims, make conditions prominent, and ensure any limits are clear.
• Supporting documents like an Employment Contract for bonuses and a Privacy Policy for referral programs help reduce disputes and keep your offers enforceable.

If you’d like a consultation on drafting or reviewing unilateral offers and making your business agreements rock-solid, reach out to us at 1800 730 617 or team@sprintlaw.com.au for a free, no-obligations chat.