The flow and heat transfer phenomena in the intake port of a spark ignition engine with port fuel injection play a significant role in the mixture preparation process, especially at part load. The backflow of the hot burned gas from the cylinder into the intake port when the intake valve is opened breaks up any liquid film around the inlet valve, influences gas and wall temperatures, and has a major effect on the fuel vaporization process. The backflow of in-cylinder mixture with its residual component during the compression stroke prior to inlet valve closing fills part of the port with gas at higher than fresh mixture temperature. To quantify these phenomena, time-resolved measurements of the hydrocarbon concentration profile along the center-line of the intake port were made with a fast-response flame ionization detector, and of the gas temperature with a fine wire resistance thermometer, in a single-cylinder engine running with premixed propane/air mixture. These measurements are used to define the extent of the backflows of gas from the cylinder into the intake port and the mixing that takes place between these backflows and fresh mixture. Hydrocarbon measurements were then obtained in the intake port with liquid fuel injection at selected timings with respect to the engine valve events. It is shown that substantial fuel vaporization takes place in the port, the amount depending on residence time and inlet pressure. Significant displacement of fuel vapor upstream by the backflow which follows inlet valve opening also occurs.