Question 377734
For a sphere, regardless of what part is where,
{{{Vol = 4*pi*r^3/3}}}
Sub 61 feet for r and get the volume in cubic feet.
Multiply that by 7.5 to get gallons.
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I don't know of any tankers that carry fuel like that.  
Some LNG carriers (Liquified Natural Gas) have the LNG in spherical tanks, tho.