  There are three parameter degeneracies inherent in the three--neutrino
analysis of long--baseline neutrino experiments. We develop a systematic method
for determining whether or not a set of measurements in neutrino oscillation
appearance experiments with approximately monoenergetic beams can completely
resolve these ambiguities. We then use this method to identify experimental
scenarios in which the parameter degeneracies may be efficiently resolved.
Generally speaking, with two appearance measurements degeneracies can occur
over wide areas of the $(\delta,\theta_{13})$ parameter space; with three
measurements they occur along lines in the parameter space and with four
measurements they occur only at isolated points. If two detectors are placed at
the same distance from the source but at different locations with respect to
the main axis of the beam (a detector cluster), each detector will measure
neutrinos at different energies. Then one run with neutrinos and one run with
antineutrinos will give the four independent measurements that in principle can
resolve all of the parameter degeneracies if $\sin^22\theta_{13} \geq 0.002$.
We also examine scenarios with detector clusters using only neutrino beams.
Without detector clusters, the measurement of neutrinos and antineutrinos at a
short distance and only neutrinos at a longer distance may also work.
