Yale Law School's Ian Ayres, from his American Contract Law course, examines Drennan v. Star Paving, the classic case on irrevocable offers and mistaken bids in construction subcontracting. A general contractor relies on a subcontractor's bid to prepare its own bid on a public paving job, then the subcontractor tries to withdraw after discovering it miscalculated the price. Ayres walks through how the court used promissory estoppel to bind the subcontractor despite the absence of a formal contract, treating the general contractor's reliance on the bid as a substitute for consideration. The lecture situates the case within the broader doctrine of irrevocable offers, explaining why courts protect the reliance interests of parties who build bids on top of other bids. It is a compact, doctrine-focused session aimed at students working through the bargain relationship unit of contract law.