The phase behavior of ABC triblock and AB diblock copolymer melts is investigated by self-consistent field theory, while allowing for (among other candidates) the orthorhombic Fddd (O70) network phase identified in recent experiments with poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblocks. Predicted phase diagrams for triblocks similar to ISO contain an O70 phase bordered by gyroid, lamellar, and alternating gyroid phases, in agreement with experiment. The O70 network is also found to be stable in diblock melts within a narrow region that overlaps the weak segregation end of the gyroid region found in previous calculations.