Transient filtration combustion waves formed in a porous matrix of randomly arranged alumina pellets are studied experimentally for rich and ultra-rich methane/air waves with oxygen enrichment and depletion. A single filtration velocity (12 cm/s) was used and the mixture equivalence ratio was varied from 1 to 3.5. The air and oxidizer content were adjusted to retain the filtration velocity constant for each equivalence ratio. Six oxidizer compositions (10%, 15%, 21%, 25%, 30%, and 35% O-2) were comparatively analyzed focusing on combustion temperatures, combustion wave velocities, major and minor products of combustion. The studied range of equivalence ratios covered the underadiabatic (upstream) and superadiabatic (downstream) regimes of transient filtration waves where combustion temperatures are less than and greater than adiabatic temperatures, respectively. 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.