The technique of velocity modulation spectroscopy has recently been combined with cavity enhancement and frequency modulation methods into a technique called noise-immune cavity-enhanced optical heterodyne velocity modulation spectroscopy (NICE-OHVMS). We have implemented NICE-OHVMS with a cw-optical parametric oscillator (OPO) tunable from 3.2 to 3.9 mu m, and used it to record spectra of the R(1,0) and R(1,1)(u) transitions of the v(2) fundamental band of H-3(+). The high optical power and cavity enhancement enable saturation of rovibrational transitions, which allows for line center frequencies to be measured with a precision of 70 kHz. (c) 2012 Elsevier B.V. All rights reserved.