In our area (where oil tanks were once used), the onus to identify whether there is a tank (assuming it's not obvious) on the premises falls on the buyer. The buyer's inspector identified that the house used to use oil, but has found no trace that an oil tank still exists. It's highly likely that when the oil furnace was removed, the oil tank may have been removed, or filled in with sand.
I would say that if they'd like to pay for ground penetrating radar, or some kind of probe, they're welcome to do so... and, of course, if they find a tank the onus may fall on you to remove it (or negotiate some of that cost).
Here are two direct link: http://www.inspect-ny.com/oiltanks/tankaudt.htm
How to Find Underground Oil Tanks - Onsite Inspection of Properties for Evidence of Buried Oil Tanks
How to Locate, Inspect, Test and Repair your Home Heating Oil Tank
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Typically searches for an underground tank would be done by ground penetrating radar/sonar, magnetic sensors or petroleum/hydrocarbon probes. Before getting too involved consult with your professionals to see how to best address this issue and how to proceed.
Hope that helps
1. underground on the side of the home nearest the furnace
2. in the cellar
3. above ground, outside generally near the furnace
A heating contractor could likely evaluate this and show you signs of where the storage container was located. Or have someone with a metal detector do a sweep of the area around your home.
It's our experience that the majoriy of oil storage facilities in the northeast are located in the cellar.
The Eckler Team