Very interesting question- and important to try and clearly resolve what you are comfortable with now - as you can include your resolution in the negotiations with the seller.
Both fuels will work but gas is preferred. Though the tank is above ground, oil will increasingly affect the resale value of your house. More natural gas is being discovered locally all the time- can we assume oil prices will keep raising.
See if you can get both a lower price for the house because of the oil and a Sellers concession to offset your closing costs and use the $$$ to replace the oil with gas. Approximate cost $7,500/9,000 including removal and anything additional like a exhaust lining.
All that said, oil does work and if the house is such a good deal- you can buy now and consider these options later.
If you are working with an agent, get some advice on all this- if not, consider getting an agent. You might be better off to have your own buyer's agent to eliminate conflicts.
Very best of luck! Best wishes for a Happy New Year!