Most QS filters are made by Purolator except for a few oddballs that might be made by FRAM.
Let me give you a little filter history.
In 1985 the Pennzoil Corporation owned the Purolator Filter Company and all Pennzoil filters were made by Purolator. At that time, FRAM made QS filters.
For some reason in 1989, Pennzoil sold Purolator to someone else (can't remember the name). Still believe that was a dumb move on our part.
Anyway, at that time FRAM was the number one selling filter in the country, and in the installed market, Pennzoil was number two. The new owners of Purolator could not keep up with our demand so we struck up a deal with FRAM.
Now, since QS was our number one competitor at that time, they would not consider having FRAM make both filters, so they cancelled their FRAM contract and signed with Purolator.
And as they say, the rest is history (almost).
Since Pennzoil bought QS and then Shell bought both of us, our filter volume has really grown. There is no one mfg that can supply all Pennzoil, QS, and Shell brand filters that are sold in North America. Pennzoil filters sold in the Southwest and Southern states are most likely made by FRAM. The Pennzoil filters sold in the Midwest are a mix of FRAM and Purolator. The Pennzoil filters sold in the Northeastern states that border Canada are probably made by Purolator. I believe most Pennzoil filters sold in Canada are made by Purolator.