There is an old joke that “an oral contract isn’t worth the paper it’s written on”. That’s a reference to the fact that it can be very difficult to prove that an oral contract exists, let alone what the terms are. Absent substantiating proof of the terms of the contract, a party may be unable to enforce the contract or may be forced to settle for less than the original bargain. Thus, even when there is no opportunity to draft a formal contract, it is good practice to always make some sort of record, signed by both parties, to memorialize the key terms of the agreement.
At the same time, under most circumstances, if the terms of an oral contract can be proved or are admitted to by the other party, an oral contract is every bit as enforceable as a written one. There are, however, “statute of fraud” laws which hold that some contracts cannot be enforced unless reduced to writing and signed by both parties.
Please note that, although sometimes an oral contract is referred to as a “verbal contract”, the term “oral” means “spoken” while the term “verbal” can also mean” in words”. Under that hyper-technical definition, all contracts are “verbal” which only confuses the issue. If you mean to refer to a contract that is not written, although most people will recognize what you mean by “verbal contract”, for maximum clarity it is helpful to refer to it as an “oral contract”.