Should I have an Oil Tank test performed? Basically, the way an oil tank is tested is an inspected will put a valve on the tank and pump air into the tank, increasing the pressure in the tank. They then come back and see if the pressure dropped. If it did, then there is a leak somewhere in the system. If you are buying a home that has an underground oil tank, you should have it tested. The only way to remedy an area that has had oil leaching into the ground is to excavate the ground and remove all contaminated soil. Depending on how long the leaching has been going on will determine how far it has leached. The costs of this remedy could be in excess of $20,000 or higher. If you do purchase a home with an underground oil tank, you might want to consider having it removed and have an above ground tank installed when you can afford it.