An oil slick in the ocean is a thin layer of oil covering a large area, many square kilometres in extent.
The variables needed for this problem are:
- the area the spill covers
- average thickness over that area.
How do we measure the area spill?
Usually, this is done with the help of satellite imagery (a line is traced around the visible edges of the slick and the area inside that boundary is computed)
A good rule of thumb is to try to estimate the minimum volume, i.e - we try to estimate the minimum average thickness. Reasonably, this can stand at about 1 micron, or 0.000001 meters.
If there is an observed slick of oil covering 1 km^2, then the minimum volume of the oil covering this surface can be calculated in meters:
1000 m * 1000 m * 0.000001 m
Or, 1 * 10^6 m^2 * 1 *10^-6 m
Or, 1 m^3
Substitute 1 km^2 for any other area to and multiply with 1 micron to get the minimum estimate of the volume for an oil spill.