compare price per btu. even though oil seems expensive it has way more btu's available so it comes out cheaper. i work on all three (oil,gas, and propane) and have yet to find that it is cheaper in the long run for a customer to switch to either type of gas. 140000 btus or 91000 btus.... easy choice for me. gas might be cheaper but you'll use more of it negating any savings. spend your money modernizing the oil system you have and you will be very happy