[en] General gaseous detonation propagation phenomena are briefly discussed. The importance of cellular structure and cell size to detonation initiation, transmission and failure is emphasized. Experimental measurements of cell size lambda for hydrogen-air-carbon dioxide mixtures are presented; the hydrogen/air volume ratios range between 0.16 and 1.5 and the carbon dioxide mole fractions are 0, 0.05, 0.10 and 0.15. Cell sizes are a minimum for both diluted and undiluted hydrogen-air mixtures near stoichiometric (i.e., hydrogen/air = 0.4). Minimum cell sizes for carbon dioxide mole fractions of 0, 0.05, 0.10 and 0.15 are 1.51, 2.05, 4.2 and 15.0 cm, respectively. Results of large- and small-scale critical tube diameter (d/sub c/) measurements are presented and show good agreement with the empirical scaling law, d/sub c/ = 13 lambda. Mean detonation velocities and pressures have been measured and compared to the theoretical Chapman-Jouguet values