With fuel storage it is very important that the internals of the tanks are coated. The reason for that is that fuel and oil is lighter than water, so all the water drops to the bottom of the storage tank and it is very corrosive. The bottom area of a tank is often contaminated with "chlorides"...in other words, "salt", particularly in crude tanks so it is very, very corrosive. What that means is the tank floor and normally 3 ft up the walls is coated.
It is crucial that surface preparation is top class, to avoid re-work and costly "tank-downtime" to re-coat a failed tank floor. And, it may be the Contractor who pays!