Honestly, I doubt ever.
There really is no good reason for it either. I'm buying conventional 5W30 oil at $2.30 a qt from my supplier, I'm reselling it at $4.17 a qt. My full synthetic really went down, it's at $2.49 a qt and I sell at $7.49 to $9.49 a qt. I have a long way to go to make up for those $19.99 oil changes just to get traffic in the door. I'm used to buying oil in bulk, I mean I buy several hundred gallons at a time. I went to buy a quart of oil at a PepBoys for my sons car a few weeks back, $6.00 a qt! I thought real hard about adjusting my oil prices.
But it's the same thing for diesel, K1 and propane, from what I understand these are all easier and cheaper to produce from crude (correct me if I'm wrong) than gasoline, yet they cost way more.