High-pressure tanks are class MC 330 or MC 331. They are used to transport liquefied gases and high vapor pressure materials.

These trailers are high-pressure tanks used to transport liquefied compressed gases such as propane and ammonia. They have a distinct appearance with rounded ends (heads), are painted white to reduce heat absorption (minimum top 2/3 of container), a bolted inspection plate located at center or top rear of the tank, and bottom loading/discharge valves. The pressure rating on these tanks is 100-500 psi. This type of tank truck can be seen either as a separate trailer or built onto a truck chassis known as a “bobtail” for residential propane delivery.