We report results on nuclear spin symmetry conservation studied by high resolution spectroscopy of relative line intensities for the A and E nuclear spin isomers of symmetric top molecules CHD3, CH3D, CH3F, and (CH3Cl)-Cl-35 in supersonic jet expansions with He and Ar as carrier gases. Infrared absorption spectra were measured around 3000 cm(-1) by an infrared (lead salt) diode laser and a continuous wave IR-OPO (infrared optical parametric oscillator) locked to a frequency comb. A detailed analysis of the R(2)-line intensities of the CH-stretching fundamental shows that nuclear spin symmetry is conserved for CHD3, CH3F, and (CH3Cl)-Cl-35 during the expansion. For CH3D, a small contribution from nuclear spin symmetry relaxation cannot be excluded completely under our experimental conditions.