  We have measured the electrical resistivity, thermoelectric power, Hall
coefficient, and magnetoresistance (MR) on single crystals of
PrOs$_{4}$Sb$_{12}$, LaOs$_{4}$Sb$_{12}$ and NdOs$_{4}$Sb$_{12}$. All the
transport properties in PrOs$_{4}$Sb$_{12}$ are similar to those in
LaOs$_{4}$Sb$_{12}$ and NdOs$_{4}$Sb$_{12}$ at high temperatures, indicating
the localized character of 4$f$-electrons. The transverse MR both in
LaOs$_{4}$Sb$_{12}$ and PrOs$_{4}$Sb$_{12}$ tends to saturate for wide field
directions, indicating these compounds to be uncompensated metals with no open
orbit. We have determined the phase diagram of the field induced ordered phase
by the MR measurement for all the principle field directions, which indicates
an unambiguous evidence for the $\Gamma_{\rm 1}$ singlet crystalline electric
field ground state.
