I've seen a lot of references lately to 5.1 jugs. In the past, I used to always pick up 5qt jugs of M1 at Wal-Mart. These jugs at the time we're just labeled as 5qts. It's been 3 years now since picking up jugs because I built up a stash of single qts. Now, I know some lubes are now sold as gallons, and then there's the 5.1 jugs. So, is the 5.1 reference refer to jugs contain 5qts in one jug or 5qts + 1qt in a jug(=6qts total, which would be perfect for me, and a senseable packaging move as oil sumps are getting larger).