The critical parameters for propane were determined using an Automation Products Dynatrol Detector. The Dynatrol is a system of coupled vibrating masses, whose resonant frequencies are functions of the density of the fluid surrounding one of the masses, namely the paddle which can be immersed in a test fluid. If the paddle is partly surrounded by liquid and partially by vapor, the resonant frequencies are measures of liquid level. An experimental cell was filled at room temperature with propane such that two phases existed. The paddle of the Dynatrol was located in the cell such that, as the cell was rotated, the paddle was immersed first in the vapor phase, next in the liquid phase, and finally partially in both phases. The temperature of the cell was raised and the amount of propane in the cell adjusted so that the Dynatrol frequencies indicated that the cell was half-full of liquid. If the interface of the two phases disappeared at the half-full point, the point of interface disappearance was the critical point. By determining the amount of propane in the cell and the cell volume, all critical parameters were determined. The values obtained are shown below.