The western Amazonian oryzomys occurs in the western Amazon Basin. In one Peruvian reserve, it was captured most often in forest, but that local pattern is not assumed to define the species everywhere.
Its dorsal fur ranges from dark brown to reddish brown, with variation even among animals from the same grid. The underside appears grey, with white hair tips.
At the Peruvian reserve it was captured in several habitat types and more often in forest. Ground traps were used, with some captures in traps placed on fallen logs.
An extinction-risk assessment has not been added yet.