The results of the investigation are presented in two parts. Part I, given in this paper, presents the experimentally measured coexisting densities and vapor pressures for the refrigerants R-22 (chlorodifluoromethane), R-134a (1,1,1,2-tetrafluoroethane), and R-124 (1-chloro-1,2,2,2-tetrafluoroethane) from 300 K to near their respective critical points. In addition, compressed liquid and supercritical densities were measured for R-22 and compared to literature values. The compressed R-22 densities agreed within experimental error with those of Kohlen et al. (Kohlen, R., Kratzke, H. and Muller, S., 1985. Thermodynamic properties of saturated and compressed liquid difluorochloromethane. J. Chem. Thermodyn., 17 : 1141-1151). Considerable discrepancies were found in the literature for R-134a and R-124 coexisting densities and vapor pressures. For both R-134a and the R-124, at least one set of data from the literature agreed with our results. The analysis of the measurements to determine critical densities which are internally consistent with our experimental measurements is presented as Part II (Van Poolen, L.J., Niesen, V.G., Holcomb, C.D. and Outcalt, S.L., 1994. Critical densities from coexisting density data : application to refrigerants R-22, R-134a, and R-124. Fluid Phase Equilibria, in press) in a separate paper.