Opinion needed about working underground oil tank in northern NJ

[Hui Song]

Oil tank in old house is common here in New Jersey. I tried to avoid buy a house with oil tank before. Right now, a old house with working underground oil tank accept my lowball offer. I am debating with myself about this deal. I have 3 days attorney review time to make final decision. The house is for sale “as is”. But my offer dies has inspection contingency. I should able to pull out of the deal if I find oil tank leak. 

Does anyone in BP have experience of dealing with working oil tank? Which oil tank leaking testing company do you recommend? Is that test reliable? If I purchase this house, should I keep using the oil heating system? If I convert it to gas, should I keep the tank underground or take it out? Any suggestions will be greatly appreciate.