A primary consideration in designing new backbone optical network segments is the total data capacity of each fiber span. We compare the wavelength-division-multiplexed capacity of conventional single-mode fiber (SMF) and nonzero dispersion shifted fiber by measuring performance versus channel spacing in 4 x 80 km transmission of five 10-Gb/s channels at the nominal commercial erbium-doped fiber amplifier power specification of 9 dBm/ch, The achievable capacity is found to be more than four times greater in conventional SMF.