The present invention relates to a heterogeneous silica/carbon black-filled rubber compound and a process for making the same. The rubber compound has improved (lower) electrical resistivity compared to homogeneous silica-filled rubber compounds. The process comprises (a) intimately dispersing from 30 to 60 phr of a silica filler and 5 to 80 phr of a carbon black in a first rubber to form a first nonproductive compound; (b) intimately dispersing curatives in said first nonproductive compound to form a first productive compound; (c) separately intimately dispersing from 20 to 100 phr of a silica filler in a second rubber, which is different from said first rubber, to form a second nonproductive compound; and (d) intimately dispersing curatives in said second nonproductive compound to form a second productive compound; and (e) mixing said first productive compound with said second productive compound to form a heterogeneous silica/carbon black-filled rubber compound.