Last I knew, Pennzoil was a Group II+ base mineral oil ... and has been for several years. Look on their bottles for the "Pure Base" label which means their Group II+ level of refining.
This is the highest level of refining of a mineral oil. Any higher than that (Group III) and it is deemed a "synthetic."
Valvoline uses the more common and less refined Group II ... and even then they only switched to that in 2001 or so from Group I which the industry is getting away from for use in new cars.
Also, Pennzoil uses a much more robust additive package ... more molybdenum ... and boron as well. These are powerful anti-wear compounds used in conjunction with ZDDP (zinc phosphate).
Valvoline All-Climate has always used a skimpier additive package than most oils. This remains true today but they have beefed it up some to meet the new SM standards.
But people still like Valvoline (in general) for two reasons:
1) They advertise more (especially in racing).
2) The old, old rumor/myth that Pennzoil leaves a waxy build-up in engines.
While there is no "bad" oil I'll take the Pennzoil any day. Either Pennzoil or Chevron Supreme which is formulated similarly. Havoline is another top choice as they use the same additive package as Chevron ... but I believe they still use the slightly less impressive Group II base oil.
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--- Bror Jace
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