2002 Nissan Altima oil

For a leak that bad you might consider renting a smoke machine. With that you can inject white, non-toxic smoke through the dip stick tube, then watch where it sneaks out. For slower leaks, wash the area, then add a small bottle of dark purple dye to the oil. As soon as you see some oil leaking out, search with a black light. The dye will show up as a bright yellow stain that you can follow back to the source.

The most common things to leak that badly are the oil pressure sending unit, loose drain plug, and loose oil filter.