The recommended oil grade for a 1995 Mercury Cougar XR7 V8 depends on your location and the operating temperature. The owner's manual is the definitive source. However, a common recommendation for that era and engine type (likely a 4.6L V8) would be
5W-20 or
10W-30.
Crucially: Check your owner's manual. The recommended oil grade will be specified there, taking into account the climate where you live. Using the wrong grade can damage your engine.