Abstract Dilute laminar expanded polystyrene particle–oil flows in a vertical pipe were studied using a three-dimensional particle image tracking (PIT) method. The particle volume fraction profiles and other flow properties for the upward fully developed flows were measured. The experimental results showed that the particles in both the large and small particle and oil flows have a wall-peaked distribution similar to those of near-spherical bubbles in laminar bubbly flows. The ordered particle distribution structure consisting of particle clusters and its transition to disordered flow structures were observed. Comparisons between the bubble and particle volume fraction profiles indicate that the major difference of two-phase flow properties may result from bubble deformation.