Densely distributed, aligned carbon nanotubes were grown on Co-covered W wires by dc-plasma-enhanced chemical vapor deposition with a mixture of acetylene and ammonia as precursors. Each nanotube was capped with a Co carbide particle. The diameter of the nanotubes ranged from 20 to 130 nm, and their average length was about 5 mum. Their field emission characteristics, measured in a modified ultra-high vacuum scanning electron microscope, were analyzed by a statistical field emission model developed for aligned carbon nanotube film cathodes. An indirect method was thus established to obtain the average electrical parameters of the film using only a limited amount of experimental data.