I was on the design team for a couple gasoline/diesel truck loading stations years ago. Most 18 wheeler type tanker trailers are 9~12,000 gallons. Sometimes up to 14,000 gallons. You will have to show me one that is over 32,000 gallons.
Here is a link to several for sale.
http://www.truckpaper.com/list/list.aspx?catid=64&Manu=HEIL&bcatid=28
Many images of the trucks.
http://tinyurl.com/o9xncxa
How much fuel does a tanker truck hold?
https://answers.yahoo.com/question/index?qid=20080701213522AAj6ZCx
FTA: A regular semi-trailer with two axles under the rear and it hooks to a regular 3 axle road tractor usually has a 9500 gallon capacity, but can only legally haul about 8500 gallons due to weight laws.
In some western states, you will see trucks that have a tank on the truck and pull a long 4 axle trailer behind that. These truck/trailer combinations have the capacity of 11,500 gallons and can weigh as much as 105,000 pounds when fully loaded.
Fuel tankers have compartments in them so that they can carry different products at the same time. Think about how a gas station is laid out. They usually have Unleaded Regular, Unleaded Premium as a minimum of products and may have a middle grade Unleaded fuel as well as Diesel. The tanker may have as many as 6-7 compartments, or separate “tanks” within the tanker truck itself. Each compartment can hold between 500 - 2500 gallons. This is so when a gas station orders a fuel delivery, it gets as much product of each as the storage tanks will allow, there by getting the best utilization of the truck as possible. Depending on how far the fuel has to be transported determines how much it costs to ship it. It will cost the same if it has 1000 gallons or 11,500 gallons, so they try to ship a full load whenever possible.