Each state has its own set of laws governing the validity of prenuptial agreements. For example, in Arizona, the Arizona Revised Statutes provide:
A premarital agreement must be in writing and signed by both parties. The agreement is enforceable without consideration.
The agreement becomes effective on marriage of the parties.
The agreement is not enforceable if the person against whom enforcement is sought proves either of the following:
The person did not execute the agreement voluntarily.
The agreement was unconscionable when it was executed and before execution of the agreement that person:
Was not provided a fair and reasonable disclosure of the property or financial obligations of the other party.
Did not voluntarily and expressly waive, in writing, any right to disclosure of the property or financial obligations of the other party beyond the disclosure provided.
Did not have, or reasonably could not have had, an adequate knowledge of the property or financial obligations of the other party.
If a provision of a premarital agreement modifies or eliminates spousal support and that modification or elimination causes one party to the agreement to be eligible for support under a program of public assistance at the time of separation or marital dissolution, a court, notwithstanding the terms of the agreement, may require the other party to provide support to the extent necessary to avoid that eligibility.
An issue of unconscionability of a premarital agreement shall be decided by the court as a matter of law.
If a marriage is determined to be void, an agreement that would otherwise have been a premarital agreement is enforceable only to the extent necessary to avoid an inequitable result.
While premarital agreements must be in writing, some state courts have enforced oral premarital agreements where the parties sufficiently performed the oral agreement to take it out of the statute of frauds.