It's a storeroom for fuel oils and lubricants such as Vale Oil, Superheated Oil, Flange Oil, and Lamb Oil prior to electicity being brought into the area.
To the right of the Oil House is the Engine Shop (just outside of the picture) and behind it is the Machine Shop & Roundhouse. JUs tcheck the offical desction and it also was the place where they stored Lamp Oil for the headlights of the locomotives. This is truly the what the building is called and used for still today. Built 1903.
Galena, IL Station: A view of Galena from the station: Views from a ferry ride on Lake Superior... Steel mill: Paper Mill: New Mexico Church ruins just north of the track in Abo Canyon: