Oil leak 2000 alero, just replaced plug, not it, leaked out all the oil after I drove it 20 miles, please help, could it be a gasket or what

You could have a defective oil filter, You put the oil filter on with out wetting the rubber o-ring with oil, you accidentally doubled up the new rubber o-ring deal with the old o-ring seal, the filter you put on had no seal on it, the seal popped out of the groove and was cut during installation, or you put on the new drain bolt on with no gasket/washer or a damaged/bent/used sealing washer instead of a new sealing washer.

Check the oil filter. The old gasket might be stuck on the engine (two gaskets stuck together), or the new gasket might be defective, misaligned or missing.

4 CYLINDERS ENGINE OIL LEAKS WILL BE AT OIL FILTER GOT HOLE OR OIL FILTER SEAL DAMAGED OR OIL PRESSURE SENDING UNIT IF YOU REPLACE OIL PRESSURE SENDING UNIT YOU NEED WRAP LAYER OF TEFLON TAPER ON OIL SENDING UNIT THREADS TO KEEP OIL FROM LEAKING OUT.NOW IF YOU HAVE V 6 ENGINE OIL WILL LEAK FROM OIL FILTER OR SEAL DAMAGED OR FILTER TOO LOOSE TIGHTEN LITTLE MORE WITH HANDS AND A RAG.CHECK OIL PUMP DRIVE GEAR O RING ON TOP ENGINE WHERE DISTRIBUTOR USE TO BE I HAVE SEEN OIL POUR OUT FAST IF OIL PUMP DRIVE GEAR O RING SEAL DRY UP CRACK YOU WILL LOOSE OIL QUICKLY.YOU NEED ADD CORRECT AMOUNT OF OIL IN ENGINE RAISE UP CAR UP A LITTLE CRANK ENGINE FOR FEW MINUTES WITH EMERGENCY BRAKE ON LAY UNDER CAR SEE WHERE OIL LEAKING AT FIRST LOOK AT OIL FILTER, THEN OIL PRESSURE SENDING UNIT. LOOK FOR STEADY STREAM OIL COMING DOWN FROM TOP BACK SIDE OF ENGINE IF SO OIL PUMP DRIVE GEAR LEAKING O RING SEAL CRACKED FAILED LEAKING OIL.I WOULD NOT DRIVE UNTIL FIX BECAUSE LOOSE TOO MUCH OIL WILL COST YOU ANOTHER ENGINE.