Pressure fluctuations within a bed of Type D particles (coarse sand, long grain rice, red spring wheat, 10 mm glass beads, pearl barley and whole peas) were measured at various bed heights. Analysis of the pressure fluctuation profiles leads to correlations that predict the minimum slugging velocity and slugging frequency, within experimental ranges. Results reveal that past correlations have little success in predicting the slugging characteristics for large particles. Particle shape plays an important role on the type of slug formed and therefore on the values of slugging frequency and minimum slugging velocity. Large particles with low sphericity formed wall slugs with high slugging frequencies and required the greatest amount of excess air to achieve slugging.