Juan emailed his neighbor Joan offering to sell her a parcel of real estate for $150,000. After mailing the letter, Juan had second thoughts and changed his mind.

Juan has made a firm offer and cannot revoke.

Juan must keep the offer open for a reasonable time because this is an option.

Under the doctrine of promissory estoppel, Juan can't revoke the offer.

Juan can revoke the offer any time before it is accepted by Joan.