Please read this short but informative background on the PADD system from the Energy Information Administration:
Originally created during World War II for the purposes of regional rationing of gasoline supplies, the Petroleum Administration for Defense Districts (PADDs) are still utilized today to track regional movements of crude oil and (particularly) petroleum products in the United States. While the PADD system might seem a bit archaic, studying the movements of petroleum products between the PADD regions is useful for understanding how these markets are segmented in the United States. Figure 2.5 shows a map of the PADDs with the locations of oil refineries.
The description of the PADD system from the EIA includes some data on inter-PADD shipments of petroleum products (remember that most of these will be gasoline and the “distillates” – diesel fuel and heating oil). Figure 2.6 shows this data in visual form, again using the PADD designation map from the EIA. The figure indicates that there is substantial inter-PADD trade between the eastern states, the Gulf Coast and the Midwest. The Rocky Mountain states and the U.S. West Coast, on the other hand, are largely isolated from the rest of the United States and even from one another. Because of a lack of refinery capacity and pipeline capacity, the U.S. West Coast, in particular, has a gasoline and diesel market that is largely separate from the rest of the country. (This is also due in part to California’s gasoline standards, which are more stringent than in the rest of the U.S.)
Petroleum product pipeline maps are not available in the public domain, but you can view an image online at the following websites.