Car Talk

Why are fuel and water carrying tankers cylindrical in shape?


Many kinds of liquids are transported by road and railway. The tanks carrying these liquids are made cylindrical and not cubical. 

Why is this so?

If tanks are made in cube or cuboids, the capacity of the tanks will increase and they can hold more cargo. 

Even the large tanks used in refineries for holding petroleum products are cylindrical in shape.

This is because cylinders don’t have corners. 

Cubes and cuboids have more space, but their corners make them unsuitable for carrying fluid. 

When carrying liquids under pressure, the stress acting at a corner is more than the stress acting on the sides.

Because of this, the stress concentrates more at the corners. 

And because of this, there are more chances of a tank to buckle or break if they are made cubical. 

There are less chances for cracks in a cylindrical tank than in a cubical tank. Even the ends are made semi-spherical in modern tanker trucks.

The LPG cylinders used for cooking are also made cylindrical. 

This is not to make them roll easily. If you observe closely, you will find that the LPG cylinder is not flat bottomed. 

It has a false bottom welded to the bottom of the cylinder.

This is why all the tanks transporting liquids are made cylindrical in shape. One more advantage is that the liquids can be easily drained in these tanks.

In fact

1.)No stress concentration

A cylindrical container doesn’t have ‘weak spots’ that need reinforcing, which would translate to using more material to build the tanker. 

In contrast, a rectangle/square has corners and flat sides, which create weak points for pressure. 

In other words, a rectangle-shaped container would fail faster than a cylindrical one upon experiencing a great deal of pressure.


The stability of the vehicle, especially one carrying liquids like oils and liquefied flammable gases, is of paramount importance. 

As such, you want to choose a shape whose center of gravity is as close to the ground as possible. 

Rectangles and squares are poor choices in this regard, as the center of gravity of a rectangular tanker would be at a greater height than that of a cylindrical tanker.

Cylindrical tankers offer a low center of gravity, which is good news for the stability of the truck. 

3.)Liquid extraction and maintenance

A cylinder, as you can imagine, is more favorable when it comes to extracting the liquid contents of the tanker, as it lets the liquid funnel down to the bottom of the tank.

A rectangle, on other hand, wouldn’t be a great choice in this regard. 

This is the same reason why most bathroom sinks are NOT rectangular.

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The Engineer

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