The reactive gas phase species OPCl has been prepared in an electric discharge, and its microwave spectrum has been measured for the first time; both quadrupole and spin-rotation hyperfine splittings were resolved. The determined spectroscopic constants have been used to derive experimental values for many properties of this molecule: the centrifugal distortion constants and inertial defects have been combined with all available infrared data to determine a harmonic force field; the centrifugal distortion corrected rotational constants have been used to yield the first direct experimental determination of the OPCl geometric parameters; the Cl quadrupole coupling tensor has been diagonalized and these values have been used to obtain an approximate value for the ionic character of the P-Cl bond; and the spin-rotation coupling constants have been used to derive nuclear shielding parameters for both the P and Cl nuclei. In all cases, comparisons with the corresponding parameters determined for other phosphenous halides (OPX), phosphenous hydride (OPH), the analogous second row compounds (ONX and ONH), and other related species have been made. Some of these parameters have also been calculated using theoretical techniques; these comparisons are given where appropriate.