The oil pressure sending unit on a 2000 Buick 3800 Series II engine is located on the
passenger side (right side) of the engine block, near the front. It's typically a small, cylindrical sensor with one or two wires connected to it. You'll likely need to look closely; it might be partially obscured by other components.
A picture or diagram specific to a 2000 Buick 3800 engine would be very helpful in pinpointing the exact location. Searching online for "2000 Buick 3800 engine diagram" or "2000 Buick 3800 oil pressure sending unit location" might yield a useful image.
