FYI,

NAPA Auto Parts specializes in European motor oils. They carry a German oil called
LIQUI MOLY at 0w-30, 0w-40, 5w-30, 5w-40, and 15w-50.

I bought a Napa branded oil made by Vavoline in 15w-50 for $3.42 a quart. It's very hard to find these weights in Walmart or Autozone.