Well, with my dad being "older" and liking it 72-74* all the time, I figure it's quite a lot.
Before I moved in with my coal stove, he was using about 4 tanks a year. I'm down to about 1 now. Maybe 1.5 tanks. And the boiler only heats the living space, not the basement. Which is one of the main reasons he was using so much oil. All that cold downstairs.
Now that I moved in, the stove is in the basement so it heats both levels and the furnace only kicks on for DHW.
At the beginning of the season, I was doing the "bucket brigade" and going to my dealer weekly and shoveling my own. Roughly 160# to 200# a week. Call it 25# to 30# a day. At $285/ton that's what? 14 cents a pound?
So that's $4.20 per day or so. With oil @ $3.39 I think we can see why we all use coal.
No way I heat 1900sf on a gallon and a half of oil a day.