How much oil in the tank?

http://www.lmnoeng.com/Volume/CylConeSphere.htm

Calculator, equation, etc...

I think this is correct, not 100% sure though:

If h is the height of the oil level above ground (h runs from 0 to 2r), and r is the radius of the tank, and L is the length of the tank, then the amount of oil in the tank is given by

(PI*r^2)/2 - (r - h)*sqrt(2rh - h^2) - (r^2)*sin_inverse((r-h)/r)

then multiply that by L

I got that by taking the equation of a circle, x^2 + y^2 = r^2, solving for y

y = sqrt(r^2 - x^2)

and integrating from r-h to r.

You need to double this result because it only gives you the area of the circle in the top-left quadrant. Multiplying by H then gives the volume you need.

Edit: curse you karoma!
That theta parameter in the calculation looks a bit strange. I don't see why you would need it.

Pepsi?

Partial credit!

While you're at it, try to solve the related problem of finding the depth of oil in the tank corresponding to a given volume. i.e. try to calibrate, in litres, a dipstick for your oiltank.