32 
Because quite different kinds of products are involved, differences in the relative proportions 
of light fuel-/lubricating oil mixtures may occur, when a spill sample is compared with a 
corresponding ship sample. These may be caused by weathering (evaporation and/or 
biological degradation), i.e. processes, which effect only the light fuel oil part of the mixture. 
In addition, there is the risk of inhomogeneous distributions of waste oil of this kind, caused 
by incomplete mixing of the two products involved. 
100 
& 
v 
1 
to 
0 
10 11 min 12 
Fig. 27: GCs of a spill sample (upper chromatograms) and the corresponding bilge sample. 
For better comparability, intensities are normalized on the lubricating oil part in the 
lower right chromatogram. 
An example is given in Figure 27, where a spill sample is compared with a sample taken from 
the bilge of the suspected polluter. Obviously there is hardly any possibility to compare the 
light fuel oil part of the samples in detail, whereas high similarities in the lubricating oil part 
(Figure 28) can already be exspected (additional and identical second “hump” in the higher 
boiling region, which indicates the same mixture of two different lubricating oils). 
A in order to cope with the problem of inhomogeneous distributions of oil, 
prosecuting authorities should be adviced to take more than one sample from the 
sampling locations especially when there is the suspicion that waste oil is 
involved in an oil spill.