Having lived at Bunchrew (not Buncrewe) I don't recall oil tanks but it may have been before my time, late 70s and early 80s. We looked out onto the line about a mile North of the disused Bunchrew station. It's also not mentioned on RailBrit which is usually pretty good source of information. Be interested to see any pictures or maps if they are available?
http://www.railbrit.co.uk/Inverness_and_Ross-shire_Railway/frame.htm
I'm sure that Lairg though still has oil trains, search on Railbrit and there are some recent images.
The Highland Bitumens plant was at Culloden and I can recall passing the tankers there when on the main line trains, there would be a small flame visble sometimes which I guess would be keeping the bitumen liquid. Peco do these wagons in N gauge. http://www.geograph.org.uk/photo/2308310
Someone else also mentioned Shrewsbury Abbey Foregate, we used to visit my Gran and frequently walk the dogs on the old Potts line which joined onto the occassionally in use branch to the Oil depot in the Abbey Foregate. Highlight of my holidays would be seeing the train, always an 08, from memory they would stop and change the points at a ground frame and then have to unlock gates into the storage compound. There are pictures somewhere at my parents house of us next to the line with the train in the background. I think there was only one train a week which was why it was considered safe to walk along the line!
http://shrewsburyrht.org.uk/history/shropshire-and-montgomeryshire-railway/