1992 Buick Park Avenue Oil problems

I was driving down the road when the oil pressure gauge started jumping around. From 40 to max then all of a sudden it just fell off. I checked my oil and I was a quart low. So I added a quart. After work I checked my oil it was fine and I started driving home thinking a sensor went bad. 10 minutes later I got of my exit and my car started knocking. I pulled over immediately popped the hood and checked the oil. It was bone dry. The inside rear tires are glazed with oil. Do you think it is my rear main seal that failed and caused the lack of pressure? If not what could it be?