The dorsal fur of
Oligoryzomys flavescens consists of bright orangish-brown hairs mixed with blackish hairs, the hairs on the flanks are all orange and the underparts are yellowish-grey. The boundary between the upper parts and the underparts is indistinct, grading from one colour to the other. The head-and-body length averages and the tails averages . Skull features that distinguish this species include the long
incisive foramina (openings in the hard palate) that usually reach the first molar, and the short mesopterygoid
fossa (a depression behind the end of the palate) which does not extend as far as the third molar. ==Distribution==