I used to think that I would use all synthetic too, but this weekend I went looking for my usual Rotella T 5W-40 for my annual oil change. But all the places I went either quit selling it or was sold out. There was no synthetic 5w-40s available so I ended up with Rotell 15W-40. So instead of spending $30 for enough oil for one oil change I spent $24 for enough oil for two changes. I don't know what happened to the supply of the synthetic oils? The first place I went had Mystik JT-8 synthetic blend 15w-40 but I kept looking for full synthetic.