Alex is Sprintlaw’s co-founder and principal lawyer. Alex previously worked at a top-tier firm as a lawyer specialising in technology and media contracts, and founded a digital agency which he sold in 2015.
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Contracts sit at the centre of almost every business decision you make. Whether you’re onboarding a new client, hiring staff, or running a marketing promotion, the type of agreement you use can affect your cash flow, your risk, and how easily you can resolve disputes.
Two concepts come up a lot: bilateral contracts and unilateral contracts. They might sound technical, but understanding how they work will help you pick the right tool for the job and avoid accidental obligations.
In this guide, we’ll explain the difference between bilateral and unilateral contracts in plain English, share practical examples for Australian businesses, and flag common pitfalls to avoid. We’ll also outline the key legal documents that help manage risk as you grow.
What Is a Bilateral Contract?
A bilateral contract is the most common kind of agreement you’ll see in business. It’s created when both parties exchange promises (and each promise is the price for the other). For example, you agree to provide a service and your customer agrees to pay your fee.
Importantly, a contract doesn’t become “real” only when it’s signed. In Australia, a binding contract can be formed by words, a signature, conduct, or a mix of these-what matters are the basic ingredients of offer and acceptance, consideration, intention to create legal relations and sufficiently certain terms.
Key features of bilateral contracts
- Mutual obligations: both sides make enforceable promises to each other.
- Immediate commitments: once formed, each party must perform their side of the bargain.
- Flexible acceptance: agreeing in writing, verbally, or by conduct can all amount to acceptance (depending on the circumstances).
Typical business examples
- Service agreements with clients (e.g. a monthly retainer for marketing support).
- Supply contracts for goods or software.
- Employment paperwork when you hire staff via an Employment Contract.
Because bilateral contracts set out mutual promises, they’re ideal for ongoing relationships where you need certainty around scope, price, timelines and how issues will be handled.
What Is a Unilateral Contract?
A unilateral contract is different: only one party makes a promise, which becomes binding if someone else performs a specified act. Think of public rewards, referral incentives, or “early-bird” promos-“If you do X, we’ll do Y.”
Acceptance happens through performance, not by promising to do the act. The person performing the act isn’t obliged to start-but if they do and complete the act as specified, the offeror’s promise becomes enforceable.
Key features of unilateral contracts
- One-sided promise: the offeror makes a binding promise contingent on a specified act.
- Acceptance by performance: the contract is formed when the act is completed (unless the terms say otherwise).
- Public or open offers: often addressed to the world at large (e.g. a public reward).
Typical business examples
- Rewards (“$500 for the return of our lost equipment”).
- Referral incentives (“Introduce a friend who purchases and receive a $50 voucher”).
- Promotions and competitions (subject to your rules and Australia’s giveaway laws).
Revoking a unilateral offer can be tricky. As a general rule, you can withdraw before acceptance-but once someone has begun performance in reliance on the offer (and especially where they’re part-way through a substantial act), Australian courts may protect them depending on the circumstances and the wording of your offer. Clear terms and timing rules matter here.
Bilateral vs Unilateral Contracts: What’s The Difference?
Both contract types are useful-but they serve different purposes. Here’s how they compare in practice.
Nature of agreement
- Bilateral: mutual exchange of promises (both parties are bound once the contract is formed).
- Unilateral: one promise, accepted through performance of a specified act.
When are you bound?
- Bilateral: usually when the other party communicates acceptance (which can be by signing, words, conduct or sometimes email-see how emails can be binding).
- Unilateral: when the specified act is completed (unless your terms say acceptance occurs earlier).
Risk and certainty
- Bilateral: high certainty for both sides-good for day-to-day trading, projects and employment.
- Unilateral: flexible and promotional-good for incentives and one-off offers, but you must define the conditions with care.
Regulatory lens (for customer-facing offers)
- Any business-to-consumer offer must comply with the Australian Consumer Law (ACL)-particularly misleading or deceptive conduct rules under Section 18 of the ACL. This applies whether your offer is bilateral or unilateral.
In short, bilateral contracts give you structure for ongoing relationships. Unilateral contracts are powerful marketing and engagement tools-so long as your terms are precise and compliant.
When Should Your Business Use Each Type?
The “right” choice comes down to your goal and the level of control you need over the relationship.
Choose bilateral when you need certainty
- Ongoing client work: set scope, milestones, fees and IP ownership in a service agreement or terms of trade.
- Suppliers and partners: define quality, delivery times, warranties and liability caps.
- Hiring and HR: lock in roles, duties and protections with a tailored Employment Contract and policies.
Choose unilateral when you’re driving action
- Rewards and incentives: “Do X by date Y and receive Z.”
- Promotions: early-bird perks, limited freebies, “first 100 customers” or referral bonuses.
- Public appeals: returning lost property or information rewards.
If you run promotions or competitions, write clear terms (who can claim, how to claim, limits, deadlines) and check any licensing or advertising requirements in your state or territory. Consumer protection rules apply to all offers, especially price claims, inclusions and exclusions.
Finally, don’t overthink the label. Some offers that look “unilateral” at first can evolve into bilateral agreements if the parties negotiate or exchange promises after an initial offer. Keep communications clear and consistent.
Common Legal Issues (And How To Avoid Them)
1) Vague or missing terms
Unclear obligations, missing dates, and fuzzy pricing are a recipe for disputes. Write in plain English, define key terms (scope, deliverables, deadlines, payment triggers), and include what happens if things change.
2) Formation mistakes
Contracts don’t always require a signature to be binding. Emails, messages or conduct can sometimes create enforceable obligations. If a signature is needed, make sure the person signing has authority and that execution meets Australian requirements (consider directors signing under company rules or signing documents correctly, including electronically where permitted).
3) Acceptance and revocation in unilateral offers
With unilateral offers, acceptance usually happens when the act is completed-so be precise about the act and the deadline. If you want the ability to close the offer early or cap the number of claims, say so clearly and make the limits prominent.
4) Misleading promotions
All advertising and promotions must comply with the ACL. Avoid ambiguous claims (“unlimited”, “guaranteed”, “free”) unless they are genuinely accurate for the whole offer period. Ensure your headline claims match the fine print and keep records to substantiate them, bearing in mind your obligations under Section 18 of the ACL.
5) Silence on change control
Scope creep is common in bilateral contracts. Build in a simple variation process: what counts as a change, how it’s approved, and how it affects time and fees. This avoids disputes over “extras”.
6) Privacy and data handling
Whether you use bilateral or unilateral contracts, respect privacy and data laws. The Privacy Act 1988 (Cth) primarily applies to “APP entities” (including most businesses with annual turnover above $3 million and some smaller businesses in specific categories). If you are covered, you must have a clear and up-to-date Privacy Policy.
Even if you’re not legally required, many SMEs choose to publish a transparent privacy notice and follow good data hygiene to build trust and prepare for growth.
Use The Right Documents (Practical Toolkit)
- Client Terms or Terms of Trade: spell out scope, pricing, payment terms, warranties and liability limits in a simple, consistent framework.
- Service Agreement: for more complex or ongoing engagements, set milestones, IP, confidentiality, and change control.
- Promotion/Competition Rules: define eligibility, how to enter, how winners are chosen, caps and deadlines (align with applicable giveaway laws and advertising standards).
- Confidentiality (NDA): protect commercially sensitive information when you share it with partners or contractors.
- Privacy Policy: if you’re an APP entity, you must have one; many smaller businesses adopt a Privacy Policy as best practice and to meet customer expectations.
- Employment Contract: set duties, pay, IP, confidentiality, restraints and termination terms for staff with a proper Employment Contract.
- Shareholders Agreement: if you have co-founders or investors, align on decision-making, vesting, exits and dispute resolution in a Shareholders Agreement.
Key Takeaways
- Bilateral contracts involve mutual promises and are best for ongoing business relationships where you need certainty around scope, price and risk.
- Unilateral contracts are accepted by performance and work well for rewards, referrals and promotions-just define the act, limits and timing clearly.
- Contracts can be formed without a signature in some cases; focus on clear offer and acceptance, consideration, intention and certainty.
- Consumer-facing offers-bilateral or unilateral-must comply with the ACL, including the rule against misleading or deceptive conduct under Section 18 of the ACL.
- Only some businesses are legally required to publish a Privacy Policy under the Privacy Act; many others choose to adopt one as good practice to build trust and prepare for growth.
- Use practical documents-client terms, service agreements, promotion rules, NDAs, employment contracts and founder agreements-to manage risk from day one.
If you’d like a consultation on which contract type suits your situation-or help drafting clear, compliant agreements-reach us on 1800 730 617 or team@sprintlaw.com.au for a free, no-obligations chat.
