Using a spectral code, we have studied the time-dependent regime of three-dimensional anelastic compressible convection with depth-dependent thermal expansivity, viscosity and thermal conductivity in a wide box of size 5¿5¿1. Surface Rayleigh numbers up to 5¿106, have been considered. Very few cylindrical plumes are developed at the bottom but they join up collectively to form strong upwellings, which pulsate chaotically. Major descending flows occur in sheets which form rectangular planform at the top. The thermal and flow fields are dominated by large-scale features. The bottom 20% of the convecting layer is found to be superadiabatic. ¿ American Geophysical Union 1992