Sure there is a difference . . . about $4 a quart. If you are tight for money there is very little difference to be had from running synthetic. Run a car oil in the viscosity Kawasaki recommends, 10w40, 10w50, 20w40 or 20w50. No car oils in this viscosity range are energy conserving. If you want to spend a little more run a synthetic in the same viscosity range. I like Mobil 1 15w50 because it is widely available and relative cheap. I stay away from simi-synthetics because basically all an oil company has to do to make a semi-synthetic oil is to take a cheap oil and put one drop of synthetic oil in it.