  We examine the prospects of making a joint analysis of neutrino oscillation
at two baselines with neutrino superbeams. Assuming narrow band superbeams and
a 100 kt water Cerenkov calorimeter, we calculate the event rates and
sensitivities to the matter effect, the signs of the neutrino mass differences,
the CP phase and the mixing angle \theta_{13}. Taking into account all possible
experimental errors under general consideration, we explored the optimum cases
of narrow band beam to measure the matter effect and the CP violation effect at
all baselines up to 3000 km. We then focus on two specific baselines, a long
baseline of 300 km and a very long baseline of 2100 km, and analyze their joint
capabilities. We found that the joint analysis can offer extra leverage to
resolve some of the ambiguities that are associated with the measurement at a
single baseline.
