It's a common misconception that contracts must be in written form to hold up in court. However, oral contracts can be just as legally binding. It isn't easy to prove that an oral contract took place in most situations, which is why most people prefer to agree to contracts in writing.
Another scenario where a non-written contract could hold up in court is if it's an "implied-in-fact contract." These agreements suggest that a person's obligation is implied by their behavior or other circumstances surrounding the case. For example, if you purchase a new stove, it's implied that it will fulfill its intended function – cooking your food. The implied-in-fact contract between you and the merchandise seller has been breached if it doesn't.