Sandbox experiments are used to study frontal thrust fault spacing, which is a function of physical properties within the thrust wedge. We consider three styles of thrust progression in mono-vergent wedges: Style I, II and III. In Style I, frontal thrusts progress forelandward, maintaining a constant spacing, whereas Style II and Style III progression show increasing and decreasing spacing, respectively. The three styles are shown as a function of the following factors: basal friction (μb), initial surface slope (α) and basal slopes (β), and surface erosion. For high μb (~s0.46), thrust progression occurs in Style II when α < 2° and β < 0.5°, and in Style III when α and β are high (α > 2° and β > 0.5°). Style II transforms to Style I when the wedge undergoes syn-thrusting surface erosion. In contrast, low-basal friction (μb = 0.36) gives rise to either Style I or III, depending on the magnitudes of α and β. Conditions with α = β = 0 developed Style I, whereas Style III in conditions with any non-zero values of α and β. In this case, surface erosion caused the process of thrust progression unsteady, and prompted outof- sequence thrusting in the wedge. This study finally presents an analysis of the three styles, taking into account the following two parameters: (1) instantaneous increase of hinterland thickness (ΔHe/He) and (2) forelandward gradient of wedge thickness (δH/δx). Experimental data suggest that thrust sequences develop in Style II for low δH/δx and large δHe/He values and, in Style III as either δH/δx increases or ΔHe/He drops. © Indian Academy of Sciences.