They run out and change those price signs as soon as any spike in the price of oil goes up.
Unfortunately, when prices drop, it’ll take a week or more before you probably start to see any decrease at the pump...
In a period of rising prices you must raise retail prices in anticipation of higher wholesale prices or you will rapidly find yourself unable to purchase sufficient stock to stay in business.
During a period of falling wholesale prices, you must recover at least the wholesale price you paid plus a small margin or you will rapidly find yourself out of business. (Buy high & sell low doesn't work for long.)
It is not exactly intuitive but it is the truth.
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)