What could this huge leak be from?

I bought a 2003 Pontiac Bonneville about a month ago. It
has 125000 miles and it is in good condition. Yesterday the
low oil light came on so I checked the oil cap under the
hood and bought one quart of 10w30 like it said and put it
in. I deliver so throughout the night I drove about 60 miles
doing deliveries with no issues at all. I came back from my
last delivery and spent about a half hour in the store. When
I came out there was a huge amount of fluid under and
around my car. I checked the dip stick and it still showed oil
in the car but the transmission fluid was empty. I noticed a
trail coming from the road from where I pulled in so it
started leaking on my last delivery. I left the car there
because I was afraid to drive it. Seems like alot of fluid on
the ground to be transmission fluid. Any thoughts?