The oil pressure guage on my 2000 Jeep Grand Cherokee is registering 0. My oil was just changed and I don't see any indication of oil leaking anywhere. Could it be the sensor?

First off I wouldnt drive your car until you make sure that you have indeed oil pressure and that the gauge is a false reading, driving your car if in fact it has no oil pressure will severly damage your engine, but firstly i would check the oil pressure switch its located on the passenger side of the engine right back from the oil filter make sure the connector is clean and free from oil and corrosion if the connector appears to be in good shape take a paper clip and insert it between the 2 terminals inside the connector your oil pressure gauge should peak at 80 PSI that tells you that your gauge and all related wiring are good and in working condition, secondly remove the oil pressure switch and hook an manual oil pressure gauge up to you engine and start the engine the guage should have a oil pressure reading anywhere from 30 PSI to 55PSI depending on engine temperature if theres oil pressure on your manual gauge replace the oil pressure switch with a new unit, if you still have 0 PSI on your gauge then stop your engine immediatly and start looking at your oil pump and lubricating system for a problem.