The PATrain, also known as Mon Valley Commuter Rail, was a commuter rail service owned by the Port Authority of Allegheny County in the Monongahela Valley in the US state of Pennsylvania. Service began in 1975 when the Port Authority assumed ownership of the Pittsburgh–McKeesport–Versailles commuter trains operated by the Baltimore and Ohio Railroad (B&O) with the support of PennDOT. The Port Authority discontinued the service in 1989.