This paper presents the results of an experimental study of the countercurrent flow limitation, or flooding, performed in small reproductions of the PWR hot leg. The experiments were carried out with air and water at room temperature and low air pressure. The effects of the inclined and horizontal lengths, inclination angle of the riser, and diameter of the test section on the phenomenon were investigated. The results with partial delivery of water showed that for a fixed air velocity, an increase in the horizontal length or inclined length of the flow channel leads to an increase of the water carried over by the air. On the other hand, in pipes with larger diameters, the drag of the water is smaller. The experimental results showed small differences in the results for tests when the inclination of the riser is lower than 90 degrees. For an inclination equal to 90 degrees, the water carried by the air tends to be lower than in the other angles for a fixed air velocity. The study led also to a new correlation for the flooding.