Pennzoil SAE vs Castrol GTX/ 20 W 50

Why such a big difference in price between Pennzoil and Castrol 20 W 50? Is Castrol that inferior compared to Pennzoil? TIA

Pennzoil SAE 5 quart 20W-50 Motor Oil $34.76

Castrol 03095 GTX 20W-50 Motor Oil, 5 Quart $16.97

amazon's algorithms can price things strangely, because it appears (speculation) to take real-time demand and supply into account. I note the amazon page says only 9 left in stock. Pennzoil doesn't seem to prioritize marketing a 5qt 20w50 conventional jug (or 1 qt bottles for that matter, though 1 qt is a bit more common), you rarely see it at common physical retail stores. I can't find it as even available to order (not including third party sellers) on walmart, target, oreilly's, autozone, advance auto parts, or napa. But since there's not a lot of alternative places to buy a 5 qt pennzoil 20w50 bottle, plus the stock issue, that could be why it's priced the way it is

In contrast, a 5qt 20w50 Castrol GTX conventional jug is pretty to easy to pick up at any brick and mortar auto parts store and wal mart (the wal mart price is the same as amazon). The only 5qt 20w50 conventionals I see at stores is Castrol GTX, Valvoline white bottle, and whatever the store brand is

I'm not going to comment on the relative quality of castrol vs pennzoil, but I will say the Pennzoil is well over-priced just in terms of Pennzoil. Napa has 1 qt Pennzoil 20w50 bottles for $4.50 which appear to be the same formula (marked down from list price of $7.60 -- I understand 5 qts at the original $7.60 price would be in line with the amazon price, except you always see 5 qt oil jugs priced at a discount to to the 1 qt bottle price, so it's not really in line)

Pepboys has 1 qt pennzoil 20w50 at $3.80

Heck, I see under the comparative products on the amazon page that they have a 6 pack of 1 qt pennzoil 20w50 bottles (6 qts) for only 2 dollars more than the 5 qt jug ($36.68)

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Dallas,Tx USA
Here's my old UOA with GTX 20W50:
Yeah Amazon's algorithms are weird. I sued to buy 5 qt jugs of Pennzoil, M1, Valvoline and Red Line but lately it shows can't be shipped to Hawaii only individual or 6 pack quarts BUT Amazon Basics 5 qt jugs could be shipped.
Muncie, Indiana
20W-50 seems to have been discontinued at most retailers, it's either special order or old stock it seems, Castrol 20w50 is the only 20w50 PCMO that they seem stock at WalMart anymore, I noticed that 10w40 offerings seem to be getting slimmer too, Seems like they only stock Mobil1, QSHM, and Castrol GTX HM in 10w40 anymore, there's still some ST in stock at my local stores but it seems like maybe it won't be restocked when they sell through it.