Improved ground-based Fourier transform infrared spectroscopic measurements of the OH Meinel (M) Δ&ngr;=2 and 3 nightglow emissions revealed unexpectedly intense transitions from high rotational levels. The rotational development in the P branches of the OH M (3,1), (6,3), and (7,4) bands has been followed to the P1(N') transitions with N'=10, 12, and 13, respectively. These measurements indicate that ~10% of the OH(X,&ngr;'=7) column rotational population is typically in rotational levels with N'≥7, in sharp contrast with the corresponding local thermodynamic equilibrium estimate of ~1%. The excess high-N' population also persists in the lower vibrational states of OH(X), as evidenced by the readily detectable high-P1(N') transitions in the (3,1) and (6,3) bands and by the presence of observable R branch heads in the (4,2) and (5,3) bands. The R heads in the (4,2) and (5,3) bands form at moderately high N' and are typically much more intense than expected on the assumption of complete rotational-translational equilibration throughout the OH M source region. These new results provide strong evidence for incomplete R-T equilibration of OH(X2&Pgr;, 3≤&ngr;'≤7, J') on a column basis under typical nightglow conditions. ¿ American Geophysical Union 1993