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, a merchant can make a firm and irrevocable offer for goods under specific conditions set by Uniform Commercial Code - § 2-205. Such an offer remains unchanged even without consideration.