I've had a hard time understanding it as well. I can understand some difference, especially considering how heating oil has an effect on diesel prices this time of the year.
I have searched for articles discussing this for some time. I have not found anything of substantial comparison.
The stocks levels explain the pricing.
But I don't understand the cause for the stock level differences.
Click the charts for the data sources. Distillates demand is about steady while gasoline is rising. Production for both are about steady. Net imports seem to be steady...