As I've been told (and have not verified) but I've been told that Walmart some how holds the rights to 5 qt containers for oil. All the other places I've seen that have large containers have always been slightly off of 5 qts, either 5.25 or 5.5qts, but I've yet to see a 5qt container for sale outside of a Walmart.
Not sure how true that is, it would seem odd that a company can own the right for oil in 5qt containers, and it could simply be that I haven't noticed it in 5qt containers, so i must stress that I have not verified this information