The experimental results of air evolution research by gravity fuel flow in a pipeline are presented. The pipe-line included an inclined section and a horizontal section connected by a bend. An orifice was installed at the entrance of the inclined pipeline section. The experimental investigations were carried out at pressures ranging from 20 to 80 kPa and temperatures varying between −20°C and +20°C. A significant fuel flow drop was observed by decreasing the pressure to a certain boundary value. This effect was caused by air evolution and the formation of two-phase air-fuel flow. It was shown that the boundary pressure value corresponding to the air evolution onset depended on temperature and fuel velocity values.