The main objectives of this experimental study are to explore mechanisms controlling the onset of liquid loading and to investigate effect of well deviation on liquid loading. An experimental study of liquid loading of gas wells has been conducted with air/water flow in a 3-inch pipe at well deviations of 0°, 15° and 30° from vertical. A total of 131 tests have been carried out. Differential pressure gradient and liquid holdup were measured. Flow pattern was observed and videos were captured with a high speed video system. Critical gas velocity which defines the threshold for liquid accumulation in a well (commonly termed liquid loading) has been identified by analyzing different measurements including video captures. Results show different mechanisms for vertical and inclined pipe flows. A minimum pressure gradient criterion can be applied to determine the critical gas velocity. Well deviation angle has an effect on critical gas velocity. Performance analysis for various models has revealed their shortcomings.