The gasket between the engine block and the oil filter adapter has given out. It's a hardbody gasket with red silicon rubber seals and costs about ten bucks. The adapter is also associated with the bottom radiator hose barb, so the radiator needs to be drained before the adapter can be pulled off.
BTW: My '97 XLT 4.6L at 125K miles does not leak any engine fluid anywhere. Everything under the hood and under the engine is dusty dry. If your ride is leaking oil, it is not a "normal" condition, so dope it out and fix it.