Leaking AC compressor oil?

Recently, our 1995 Taurus GL sedan lost, all at once, about 1/2 cup of fluid from the passenger side of the engine compartment. The fluid was clear-brownish tint, thin but slick, and didn't dry on the concrete. It is not brake fluid, ATF, or PS fluid, which leaves the AC compressor as the only chunk of equipment that may be leaking in that area. Does anyone know what compressor oil looks like, and if it could all leak out at once? My wife had just started the car and was backing up when I noticed the fluid running onto the driveway.