Carbon-filled polymer blends with a triple-continuous structure, consisting of a binary (or ternary) polymer blend and carbon particles, have great potential to provide injection moldable PEM fuel cell bipolar plates with superior electrical conductivity and sufficient mechanical properties. Four carbon nanotube (CNT)-filled polymer blends, i.e., CNT-filled polyethylene terephthalate (PET)/polyvinylidene fluoride, PET/polypropylene, PET/nylon 6,6, and PET/high-density polyethylene blends, have been injection molded and characterized in terms of their microstructures, electrical conductivities, and mechanical properties. Effects of the thermodynamic driving force, rheology of the polymer blend, and injection molding conditions on the distribution of CNTs in the blends have been examined. The simultaneous improvements in the electrical conductivity and mechanical properties of carbon-filled polymer blends over carbon-filled polymers have been investigated based on the CNT distribution in the polymer blends. The results unambiguously indicate that the preferential location of CNTs in one of the continuous polymer phases in the polymer blend is highly desirable for both mechanical and electrical properties. Future directions in this emerging area are discussed.