Create panel > Geometry button > Extended Primitives > Object Type rollout > OilTank button
Create menu > Extended Primitives > Oil Tank
Tab panels > Objects tab > Oil Tank Object
Use OilTank to create a cylinder with convex caps.

Examples of oiltanks
To create an oiltank:
From the Create menu, choose Extended Primitives > Oil Tank.
Drag the mouse to define the radius of the base of the oiltank.
Release the mouse, and move it vertically to define the height of the oiltank.
Click and move the mouse vertically to define the height of the convex caps.
Click again to finish the oiltank.
Edge—Draws the object from edge to edge. You can change the center location by moving the mouse.
Center—Draws the object from the center out.

Radius—Sets the radius of the oiltank.
Height—Sets the dimension along the central axis. Negative values create the oiltank below the construction plane.
Cap Height—Sets the height of the convex caps. The minimum value is 2.5% of the Radius setting. The maximum value is the Radius setting, unless the absolute value of the Height setting is less than the double Radius setting, in which case cap height cannot exceed ½ of the absolute value of the Height setting.
Overall/Centers—Determines what the Height value specifies. Overall is the overall height of the object. Centers is the height of the midsection of the cylinder, not including its convex caps.
Blend—When greater than 0, creates a bevel at the edge of the caps.
Sides—Sets the number of sides around the oiltank. To create a smoothly rounded object, use a higher number of sides and turn Smooth on. To create an oiltank with flat sides, use a lower number of sides and turn Smooth off.
Height Segs—Sets the number of divisions along the oiltank's major axis.
Smooth—Blends the faces of the oiltank, creating a smooth appearance in rendered views.
Slice On—Turns on the Slice function. Default=off.
When you create a slice and then turn off Slice On, the complete oiltank reappears. You can therefore use this check box to switch between the two topologies.
Slice From, Slice To—Sets the number of degrees around the local Z axis from a zero point at the local X axis.
For both settings, positive values move the end of the slice counterclockwise; negative values move it clockwise. Either setting can be made first. When the ends meet, the whole oiltank reappears.
Generate Mapping Coordinates—Sets up the required coordinates for applying mapped materials to the oiltank. Default=off.
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