We present sub-Doppler heterodyne frequency measurements on 10 rovibrational transitions of carbonyl sulfide (OCS) between 2894 and 2910 cm-1. The measurements were made using a CO overtone laser which had limited tuneability through the generation of microwave sidebands in a CdTe crystal. With this technique the laser frequencies were shifted to the desired OCS transition frequencies. The transition frequencies could be measured with uncertainties less than 30 kHz (Deltanu/nu = 3 x 10(-10)) by frequency offset-locking the CO overtone laser to combination frequencies of two saturation-stabilized CO2 laser standards. The measured transition frequencies of OCS were combined with previous sub-Doppler, Fourier transform, and microwave measurements to recalculate improved calibration tables for the 10(0)1-00(0)0, 11(1e)1-01(1e)0, and 11(1f)1-01(1f)0 bands. These tables are suitable for the calibration of infrared spectrometers in the 87 THz region (near 2900 cm-1). Copyright 1998 Academic Press.