I would say China makes most of the oilfilters, just a guess,now hows that?
i would say quite poor. since joining this site ive tried tons of different branded filters for my 2 cars. i think ive used at least 1 of every filter sold in this town. ive bought frams, purolators, mobils, wixs', numerous champ labs made filters, and i have never gotten an oil filter made outside this country. maybe its just the cars i drive, but there is still PLENTY of oil filter manufacturing going on here in the U.S.
back on topic, i would guess purolator. only because they make pennzoil and quaker state (both SOPUS) oil filters tho