By "gas", do you mean propane or natural gas? Propane has always been about 15% more expensive than oil on a per-btu basis, at least here in New England, but piped-in natural gas has gotten quite cheap over the past few years, thanks to environmentally dubious fracking in Appalachia and elsewhere.

If you have natural gas service on your street, it would be economical to burn it in your boiler, assuming it doesn't cost a ridiculous amount to connect it to your house. But propane will be more expensive than oil, unless you live in an area where it is unusually cheap.