Just because a home is not currently using heating oil may not mean you have nothing to be concerned with when buying a pre-existing home. Many older homes that currently heat with electric or natural gas furnaces may have used oil heat in the past. When a homeowner switched heat sources it was not uncommon for the tank to simply be abandoned. In following years landscaping and construction changes can make the tank difficult to find. To limit their future liability, homebuyers often choose to do underground tank searches without clear evidence that the home has ever used heating oil.
If it's discovered that a leak has occurred, the tank will need to be decommissioned and a DEQ certified cleanup completed. To continue using heating oil, a new tank will need to be installed either aboveground or underground. Some choose to convert the home's heat source to natural gas and install a new natural gas furnace.
If the tank has not leaked the seller will be released from future liability for underground tank leakage. The new owner will know that the heating system is functional and can continue using the heating oil tank and furnace.