is it possible to buy heating oil in small quantities (~50 or 100 litres)

The smallest i can find it in so far is 500litres.

The house (not mine – hence i know nothing about oil!) is being sold soon and i dont want to give away £200 worth of oil if i can help it.

the 500ltrs is usually the minimum order to make it worth sending a great big truck for delivery, might be worth seeing if you can collect from their depot instead, although you'd need to have a suitable container.

EDIT: Double check that its suitable, but red diesel (tractor fuel) can I think be used as heating oil in the place of kerosene, in that case a rural filling station, somewhere a bit boaty if you live by as canal / lake / the sea or a truck stop should be able to dispense you some, so long as you have something suitable to put it in.

also, call round a few filling stations – some stock 20ltr containers of heating oil.

You cant buy heating oil from a truck/tanker in less than 500 (or occassionally 300) litre quantities. Maybe try your local heating oil distributor firm and see if the sell it in small drums?

There are domestic oil heating systems which run on gas Oil, but most are now kerosene. As gas oil is less refined, I don't think gas oil (red diesel/tractor diesel) should be put in kerosene (SBO/RBO) burners. It's possible you could get away with kerosene in a gas oil burner tho, I might be wrong.

Anyway, Like someone says, if you live in a rural area you might beable to buy drums of kerosene from an agricultural suppliers, or possibly take a drum along to a local small indie oil distribution depot.
In less rural areas, most oil distributors thesedays often just rent office space in a big refinery or massive satallite oil storage depot. In this case, there's no way you would beable to walk in with a couple of 25l drums, you wouldn't even get past the gates.

We used to have some tankers which were really small for getting up tight driveways etc. unfortunately, I can't remember what the minimum delivery was.

thekingisdead

where do you live?
a bit random I know, but just a thought as we are ripping my old oil burner out and the connected oil tank, we are gonna drain the oil out so will have small quantities available.

Find out if the new owners would like the courtesey of a filled up tank so they don't have to worry for a bit, and then if they would, then "sell" the unused onto them. Its not like they're not going to need it, sooner rather than later, and might actually be grateful not to have to worry straight away, and have the reassurance that in the middle of knowwhere, at some time like midnight on saturday, they won't lose heating/cooking (if theyhave an aga).