## Facts

- Mary Ellen Cook, a licensed real estate salesperson, worked for a brokerage as an independent contractor under a verbal arrangement.
- In March 1991, the brokerage announced an agent bonus program to retain agents, with specified commission thresholds and bonus amounts/percentages; bonuses beyond an initial $500 were to be paid at year-end.
- Cook exceeded $15,000 in commissions by April 1991 and received the $500 bonus in September 1991.
- By September 1991, Cook had earned more than $32,400 in commissions, qualifying for the highest bonus tier (30%).
- In September 1991, the brokerage announced bonuses would be paid at a March banquet and indicated an agent had to be with the company in March to receive the bonus.
- Cook remained with the brokerage through the end of 1991, testifying she did so in reliance on the promised bonus.
- Cook accepted a position at another brokerage in January 1992; the brokerage then refused to pay her 1991 bonus.
- Cook sued for breach of the bonus agreement; a jury found for Cook, and the trial court entered judgment for $24,748.89.

## Issues

1. Whether the bonus program was an offer for a unilateral contract accepted by Cook’s performance, making it enforceable.
2. Whether Cook’s substantial performance rendered the bonus offer irrevocable, preventing the brokerage from later imposing a continued-employment-to-March condition.
3. Whether alleged instructional, evidentiary, or closing-argument errors required reversal.

## Decision

- The appellate court affirmed the judgment for Cook.
- The court held the bonus program was a unilateral-contract offer accepted by performance.
- Cook substantially performed by generating qualifying commissions and remaining with the brokerage during 1991, making the offer irrevocable.
- The brokerage could not retroactively modify the offer by conditioning payment on continued employment until March 1992.
- The court rejected the brokerage’s additional claims of trial error as not warranting reversal.

## Legal Principles

- A unilateral contract is formed when one party promises payment in exchange for the other party’s performance; acceptance occurs through performance rather than a return promise.
- Although offers are generally revocable before acceptance, a unilateral-contract offer may not be revoked once the offeree has rendered substantial performance.
- Substantial performance can supply consideration that makes the offer enforceable and bars the offeror from imposing new conditions after performance has materially occurred.
- In bonus-plan disputes, an employer’s stated commission-based bonus schedule may be an enforceable offer, and continued work and achievement of targets can constitute acceptance and substantial performance.

## Conclusion

The court enforced the brokerage’s commission-based bonus plan as a unilateral contract and held that, after Cook substantially performed under the announced terms, the brokerage could not avoid payment by later adding a requirement that she remain employed until a later bonus-payment date.


Cook v. Coldwell Banker/Frank Laiben Realty Co., 967 S.W.2d 654 (Mo. Ct. App. 1998)