The short version
- A purchase order is an offer. It becomes a contract when the seller accepts it — by acknowledgement, by signature, or by shipping the goods.
- The common-law mirror-image rule and UCC § 2-207 give different answers. At common law an acknowledgement with new terms is a counter-offer; under § 2-207 it usually still operates as an acceptance and a contract forms anyway.
- Between merchants, additional terms in the acknowledgement become part of the contract unless the offer limited acceptance to its own terms, the terms materially alter the deal, or objection is given within a reasonable time.
- Where the writings never agreed but both sides performed, § 2-207(3) builds the contract from the terms the writings share, plus the Code's own default rules.
A purchase order is an offer until something accepts it
A purchase order is a document, not a legal category. On its own it is an offer to buy on stated terms — quantity, specification, price, delivery date — and until the seller does something with it, there is nothing to enforce. Buyers who believe issuing a PO commits the supplier, and suppliers who believe receiving one commits the buyer, are both wrong for the same reason.
Is there a contract yet?
The buyer has sent a purchase order. Is there a contract?
The seller has done nothing yet
No contract. The PO is an offer, and the buyer can generally revoke it before acceptance.
The seller acknowledged, signed or shipped
A contract exists. What is left to argue about is which terms it contains, not whether it binds.
Acceptance does not have to be a signature. Under UCC § 2-206, an offer invites acceptance in any manner and by any medium reasonable in the circumstances, and an order for prompt shipment invites acceptance either by a prompt promise to ship or by the shipment itself. A seller who says nothing and sends the goods has accepted. A seller who returns a signed acknowledgement has accepted. A seller who does neither has not.
What actually turns a PO into a binding contract
- A definite offer. Quantity above all — the Code will supply a missing price, but not a missing quantity.
- Acceptance by the seller, whether by signature, written acknowledgement, or performance such as shipment.
- Consideration, which the exchange of goods for money supplies automatically.
- A signed writing where the price is $500 or more, which is the threshold in the uniform text of § 2-201.
- Authority in the person who issued or accepted it — where corporate procurement most often comes unstuck.
Nothing on that list is unusual, which is the point: a PO is an ordinary contract document dressed in procurement clothing. The interesting question is never whether it binds. It is what happens when the acknowledgement that accepts it arrives carrying a different set of printed conditions.
Two bodies of law give two different answers
The classical rule is the mirror-image rule: an acceptance had to match the offer exactly, and any variation made it a counter-offer instead. Applied to a PO and a conflicting acknowledgement, that produced no contract at the writing stage. Whoever performed afterwards was taken to have accepted the last form sent — the "last shot" doctrine, which rewarded whichever party managed to fire the final piece of paper.
Article 2 of the UCC abandoned that for the sale of goods. Article 2 applies to transactions in goods, so which regime you are in is decided by what is being bought: a PO for steel is Article 2, a PO for consulting days is common law, and a PO for a machine plus its installation falls to whichever element predominates.
What changes when the purchase is goods
Common law — services
- New terms make it a counter-offer
- Performing afterwards accepts them
- The last form sent tends to win
True either way
- A PO alone is only an offer
- Silence is not acceptance
- A signed master agreement beats both
UCC Article 2 — goods
- The acknowledgement still forms a contract
- Extra terms are proposals; some stick
- Conflicting terms knock each other out
What § 2-207 actually says
Subsection (1) is the reversal. A definite and seasonable expression of acceptance, or a written confirmation sent within a reasonable time, operates as an acceptance even though it states terms additional to or different from those offered — unless acceptance is expressly made conditional on assent to those terms. So a contract forms on the buyer's terms, and the seller's extra conditions are handled separately.
Subsection (2) handles them. Additional terms are proposals for addition to the contract. Between merchants they become part of it automatically unless one of three exceptions applies.
| The test | What it means in practice |
|---|---|
| Both parties are merchants | Between businesses dealing in goods of the kind, extra terms can come in automatically. With a consumer on one side they remain proposals needing assent. |
| The offer did not limit acceptance to its own terms | One line on the PO — acceptance is limited to the terms of this order — closes the door before the acknowledgement arrives. |
| The term does not materially alter the contract | Arbitration clauses, warranty disclaimers and broad indemnities are commonly held material. Routine administrative terms commonly are not. |
| No objection was given | Objection already made, or made within a reasonable time after notice of the term, keeps it out. |
Purchase order template
Full text, free to read and copy — including the line that limits acceptance to the terms of the order, which is the cheapest single defence a buyer has in the battle of the forms.
The acknowledgement is where the second set of terms arrives
Sellers treat the acknowledgement as a confirmation. Legally it is doing four separate jobs at once, and each one changes the outcome.
Four lines that decide the outcome
The seller's acknowledgement
That last line is the quiet fix. A supplier who wants their terms to govern should not print them more aggressively; they should get the acknowledgement signed and returned, or get a supply agreement in place. Our guide to supply agreement terms covers what belongs in one.
When nobody agreed and both sides simply performed
This is the ordinary case. The PO went out, the acknowledgement came back, nobody compared them, the goods shipped and the invoice was paid. Subsection (3) covers it: conduct recognising the existence of a contract is enough to establish one even though the writings do not, and the contract then consists of the terms on which the writings agree, together with the Code's supplementary provisions.
The fix is structural, not a better form
Firms respond to this by escalating the paperwork: bolder capitals, a longer conditions block, a clause insisting the other side's terms are rejected. It does not work, because the other side is doing the same thing and neither document is being read. The only reliable answer is to take the terms out of the transactional documents entirely.
What the master agreement has to say
- The master agreement governs all purchases between the parties, whenever and however ordered.
- Purchase orders and acknowledgements are administrative only — quantity, price, specification, delivery, ship-to.
- Any pre-printed or standard terms on either document have no effect, whether or not objected to.
- A change to the master terms requires a signed written amendment naming the clause changed.
- The agreement is signed by someone with authority on both sides, and the procurement team knows it exists.
That structure is the same one used for services in a master agreement with statements of work beneath it, described in MSAs and statements of work. Where the trading relationship is continuous, a sales agreement or a supply agreement does the same job for goods, and the PO becomes what everyone already assumed it was: a number that authorises a shipment.
Who actually wins the battle of the forms
Usually nobody. The instinct that the last document sent controls belongs to the common law and does not survive Article 2, and the instinct that the terms on the back of a PO bind a supplier who never read them is optimistic in either regime. What the parties end up with is a contract assembled from what they happened to agree plus a set of statutory defaults neither of them chose.
That outcome is not always bad — the Code defaults are reasonable, and for a one-off order of stock items they are entirely adequate. It is bad when the term that vanished was the one protecting against the risk the deal actually carried: the liability cap on a component going into safety-critical equipment, the warranty disclaimer on a bespoke build, the forum clause with a counterparty three states away. Decide which of your purchases are in that category, and put a signed agreement behind those before the next order goes out. For everything downstream of it, invoice payment terms covers the document that follows.
Sources
General information, not legal advice. This guide explains how these documents and rules generally work. Law varies by jurisdiction and changes, and none of it is applied to your circumstances here. For anything consequential, consult a licensed attorney where you are.
Frequently asked
Is a purchase order legally binding?
Not by itself. A purchase order is an offer to buy on stated terms, and it becomes a binding contract when the seller accepts it — by signing and returning an acknowledgement, by confirming in writing, or by shipping the goods. Until then the buyer can generally revoke it. Once the seller has accepted, both sides are bound, and the remaining question is which terms the contract contains.
What is the battle of the forms?
It is the situation where a buyer sends a purchase order carrying its standard conditions and the seller replies with an acknowledgement carrying different ones, so the two writings never match. At common law the mismatch meant no contract formed on the writings. For sales of goods, UCC § 2-207 lets a contract form anyway and then decides separately which of the competing terms became part of it.
Does the last form sent win?
That was the common-law position, known as the last-shot doctrine: performing after receiving a counter-offer accepted its terms. UCC § 2-207 was written specifically to end it for sales of goods, so the party who sent the final piece of paper gets no automatic advantage. For contracts outside Article 2 — services, most notably — the last-shot analysis can still apply.
Do the terms on the back of a purchase order bind the supplier?
Only so far as the supplier accepted them. If the supplier accepts without objection, the buyer's terms form the contract. If the supplier replies with conflicting terms, the conflicting ones commonly cancel out and the Code supplies a default, while genuinely additional terms run the tests in § 2-207(2). Printing terms more prominently does not change the analysis.
Can a purchase order override a signed master agreement?
It should not, and a well-drafted master agreement says so expressly: purchase orders are administrative, and any pre-printed terms on them have no effect. Without that clause the position is arguable, because a later signed document can amend an earlier one. State it in the master agreement rather than relying on the order of dates.