Big difference the oil is a closed unit using filters for any intake passages, where the oil-less also has the filter for the intake but also has the bottom of the piston and sleave exposed to the elements on the compression side and has a fan that blows directly into the bottom of the sleave and piston to keep it cool. (while blowing sand and anything else in it too) the motor is still a closed unit. I'm a roofer and have gone through many oil-less thinking they would need less up-keep. I now have a oil and will never go back. Oil-less was one of the worst ideas to come out. go with oil they last forever if you treat them right.