This study investigated the cure characteristics, mechanical properties, and oil resistance of acrylonitrile-butadiene rubber (NBR) filled with 60 phr carbon black (CB) and different amounts of silica from fly ash [fly ash silica (FASi)] and precipitated silica (PSi). Loadings of CB and PSi silica in NBR vulcanizates reduced the scorch and cure times. An increase in the cure time of FASi-CB-NBR vulcanizates was probably caused by an interaction between the polarity of NBR and the metal oxide activators in FASi, which could retard the curing. The tensile modulus of NBR vulcanizates increased with the addition of CB and silica fillers and with immersion in hydraulic oil at 125 degrees C. CB exhibited a more pronounced effect on the NBR reinforcement versus the PSi and FASi fillers. The tensile and tear strengths and elongation at break decreased under thermal aging in hydraulic oil. The PSi system showed better reinforcement of CB-NBR vulcanizates than the FASi system. The hardness of NBR vulcanizates increased with CB and silica. The results in this work suggest that silica from fly ash particles could be used as an extender for cost savings in NBR compounds. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2877-2883, 2008