A measure of the difference between rack prices, as can be found in the ULSDR data, and the retail price found in the DTA data. It can be found for all areas where both sets of data are available.
This spread is particularly important to trucking company profitability. The ability of companies to capture their retail fuel costs relative to the rack price is important. During volatile times, a big difference in these prices can result in fuel surcharges being inadequate or conversely be a windfall, since the DOE retail price is a function of retail prices and wholesale prices.
It is a straight arithmetic formula that subtracts the rack price from the wholesale price. It is in $/gallon. This data is also available on the regional level set by airport code.