You should work on determining exactly how much oil your heating oil tank can hold. Even the smallest of tanks can store as much as 100 gallons. Most homes have above-ground tanks that have a maximum capacity of 275 gallons. Tanks with larger capacities are generally designed for underground storage.
Keep in mind that the listed capacity of a tank is not the actual amount of fuel that it can hold. Tanks that have a maximum capacity of 275 gallons can typically only hold 225 gallons. The remainder of the tank accounts for miscellaneous debris and air. You can get a lot of pertinent info by simply reviewing your oil delivery receipt.