When parties to a contract make promises to perform their obligations, and one party reasonably relies on the other party’s promise—but the party making the promise fails to perform, causing harm or loss to the party who relied on the promise—the party who relied on the promise to perform is said to have relied to its detriment.

This legal concept is called detrimental reliance. Detrimental reliance may serve as a substitute for consideration, and make an otherwise unenforceable contract enforceable.

Thus, detrimental reliance is a legal concept based on fairness (known as equity or equitable), and is equivalent to contractual promissory estoppel (due to the other party’s reliance, the party who did not keep its promise is prohibited from challenging the enforceability of its promise).

Detrimental reliance is not a separate tort cause of action.

In Oklahoma, the legal concept of detrimental reliance, also known as promissory estoppel, is recognized and can be used to enforce a contract that may otherwise lack consideration and be unenforceable. This doctrine applies when one party makes a promise that the other party relies on to their detriment. If the relying party's reliance was reasonable and it resulted in harm or loss due to the promisor's failure to perform, the court may enforce the promise to prevent injustice. Detrimental reliance is grounded in principles of fairness and equity, ensuring that a party cannot renege on a promise that was reasonably relied upon by the other party to their detriment. However, it is important to note that detrimental reliance is not a separate cause of action in tort; it is a principle applied within the context of contract law to address issues of fairness and to prevent unjust outcomes.