So let's see if we have this straight, for the non-expert:

Per Diem is the fee that railroads pay to each other for the use of cars owned by the payee railroad. In the STMFC days, that was $2.00 per day. The paperwork must have been fascinating in the pre-computer age; calculating how much railroad A owed to Railroads B through Z for the cars on Railroad A's property.

Demurrage is the fee that customers who receive shipments pay to the delivering railroad if they keep a freight car for longer than the "grace period" for unloading.

Two different terms, often mistakenly used interchangeably.

Peter Weiglin
Amelia, OH