The maximum duration of a standard residential lease agreement is three (3) years in Pennsylvania (68 P.S. §§ 250.201).
Leases of more than 3 years must be in writing and signed in order to be valid and not considered a tenancy at will (68 P.S. §§ 250.202). If such a lease is not signed or written, it is considered only a year-to-year lease, rather than a 3-year lease.
Verbal (or oral) leases are valid for terms shorter than 3 years, but it is recommended that all leases be in writing. It is easier to prove exactly what the tenant and landlord agreed upon if the lease is in writing.
The information for this answer was found on our Pennsylvania Residential Lease Agreement answers.