Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark-ignition engine, having cylindrical disc-shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of he flame front, A comparison has also been made with a spark-ignition engine having one spark plug at the same location. Copyright (C) 2002 John Wiley Sons, Ltd.