A 2.5L, V-6, port-injected, spark-ignition engine was modified for optical access by separating the head from the block and installing a Bowditch extended piston with a fused-silica top and a fused-silica liner in one of the cylinders. Two heads were employed in the study. One produced swirl and permitted modulation of the swirl level, and another produced a tumbling flow in the cylinder. Planar laser-induced exciplex fluorescence, which allows the simultaneous, but separate, imaging of liquid and vapor fuel, was extended to capture components of different volatilities in a model fuel designed to simulate the distillation curve of a typical gasoline. The exciplex fluorescence technique was calibrated in a separate cell where careful control of mixture composition, temperature and pressure was possible.The results show that large-scale motion induced during intake is critical for good mixing during the intake and compression strokes. High intake port velocity is important for initial droplet atomization, but does not guarantee complete mixing. Liquid wall impingement can lead to significant non-uniformity in fuel distribution near the end of the compression stroke, with high potential for producing increased hydrocarbon emissions. Finally, accurate representation of both liquid and vapor phases of the fuel and both the light and heavy components of the fuel is needed for drawing accurate conclusions from fuel distribution data.