The most important source of information about a residential tenant’s rights and a landlord’s responsibilities is the written lease agreement. Some landlords prefer oral agreements, but it is more common for them to require the tenant's signature on a written lease—and a written lease protects the tenant more than an oral agreement. Be sure to read the lease carefully before you sign it.

A residential landlord’s ability to charge late fees generally depends on the specific language in the written lease agreement; the state’s landlord-tenant laws that may limit the amount of late fees the landlord can charge and the circumstances in which they can be charged; and the state's contract law.

Contract law in most states recognizes an implied duty of good faith and fair dealing between parties to a contract, and a residential landlord who charges late fees because the tenant is an hour late paying the rent may be in breach of the landlord’s implied duty of good faith and fair dealing—unless, for example, the lease agreement specifies an hour (12:00 p.m.) of the day by which rent is due and states that time is of the essence.

In Oklahoma, the lease agreement is indeed a crucial document for outlining the rights and responsibilities of both tenants and landlords. It is highly recommended for tenants to have a written lease agreement, as it provides more security and clarity than an oral agreement. When it comes to late fees, Oklahoma state law allows landlords to charge them as specified in the lease agreement. However, the fees must be reasonable and are subject to limitations under the Oklahoma Residential Landlord and Tenant Act. The Act does not specify a maximum late fee but implies that any fee charged should be a fair estimate of the damages the landlord incurs due to late payment. Additionally, Oklahoma contract law does include an implied duty of good faith and fair dealing, which means that a landlord's actions, including the imposition of late fees, should not be arbitrary or done in a manner that undermines the tenant's rights or the purpose of the contract. Therefore, a landlord charging a late fee for rent that is only an hour late could potentially be seen as acting in bad faith, especially if the lease does not explicitly state such strict time constraints. Tenants should carefully review their lease agreements for any clauses regarding late fees and the required time of payment to understand their obligations fully.