Purolator makes Microgard oil filters.
They changed makers a few months ago. If you get a re-labeld box (one with a sticker on the box), it's a purolator. If you get one that looks new and plain, it's a Honeywell filter who also makes fram.
Fram makes them exclusively for O'Reillys. They use Racor filters internally which makes the OEM versions as well.
Microgard filters are made by fram and they go by the same number. Examle, Fram 7317 would be a Microgard 7317.
WIX makes all of NAPA's oil filters
Champion Filters (not connected with Champion Spark Plugs)
11/24/2012: I just purchased 2 MicroGard MGL2 Oil Filters from O'Reilly Auto Parts in San Carlos, CA. I told the sales prep I needed oil filters for both my 2000 Ford Expedition with a Triton 5.4L V-8 and my 2003 Lincoln Town Car with a 4.6L SOHC V-8 engine, and he said they both used the same MGL2 Oil filters. Presently, the oil filters which are inplace and need of changing are from one of those oil changers places where I will no longer go to because they always try to sell you other stuff. But, their filters are larger, longer than the squat smaller MGL2 filters. Hope this helps.
Ashland makes the oil to Kubota spec
Champion
hastings
Purolator
I have been searching on the net and found out that WIX makes the carquest oil filters. If you look at the carquest oil filter box it will say Wix Filtration.
Made by Fram.
Champion Labs.