Control of the unreacted fuel would reduce total hydrocarbons from engines, therefore it is necessary to understand the mechanism of exhaust hydrocarbons from spark ignition engines. The authors of this paper would like to pay close attention to the effects of a ring crevice. The fuel-air mixture supplied to a spark ignition engine is compressed into the ring crevice in the compression stroke. The unreacted fuel within the crevice is exhausted in the expansion stroke, if the flame cannot enter the inside of the crevice. The purpose of this work is to separate the effects of the ring crevice on hydrocarbon emission from the other effects, so that the authors have proposed an element model for estimating the in-cylinder oxidation of the hydrocarbon from the crevice. To verify propriety of the theoretical model, the authors have also carried out the experiment with the linear crevices, different from a normal ring crevice, mounted on the piston top, and have obtained the agreement of values between the experimental and the theoretical results.