In the United States, an exception is the merchant firm offer rule set out in Uniform Commercial Code - § 2-205, which states that an offer is firm and irrevocable if it is an offer to buy or sell goods made by a merchant and it is in writing and signed by the offeror. Such an offer is irrevocable even in the absence of consideration.
In the United States, there's an exception to the general rule regarding firm offers made by merchants as outlined in Uniform Commercial Code - § 2-205. This allows such offers to be considered firm and unchangeable regardless of whether they include consideration.