Dopant low-n Rydberg states perturbed by dense CF4 and CH4 were investigated using vacuum ultraviolet photoabsorption spectroscopy at noncritical temperatures and on an isotherm near (+0.5 degrees C) the perturber critical temperature. A full analysis of these data using semi-classical line shape theory was performed. The perturber induced energy shift was extracted from the simulated bands and demonstrates a perturber critical point effect on the energy of low-n Rydberg states in these molecular fluids. (C) 2009 Elsevier B. V. All rights reserved.