I can give you the lay definition, what it would essentially mean, but some of the other industry experts could probably talk to the motivation and how it actually happens.
As the price of crude oil would increase, retailers and other distributors would see what the future cost of replacing, roughly speaking, their inventory would be. So if crude oil is increasing rather quickly, the cost of buying gasoline in the future is also going to rise because refiners are going to be buying at a higher cost. Therefore, they are thinking about how much it is going to cost to replace the inventory they have. There are other huge aspects within that in terms of gasoline and wholesale, which others could probably speak to, but the first-in, first-out, how much it costs to get the replacement, is the simplest part of the concept.