33 
Fig. 28: Hopanes and steranes of a spill sample (upper chromatograms) compared with the 
bilge sample of the suspected polluter (same samples as in Fig. 27). 
Since heavy fuel oils and lubricating oils normally overlap completely in the higher-boiling 
region, the detection even of smaller amounts of lubricating oil in HFO is more difficult. 
In most cases, the typical unresolved “hump” of the lubricating oil can be detected by GC- 
screening in bilge oil or sludge samples also of ships, which use HFO (Figure 29). 
Fig. 29: Gas-chromatograms of HFO-samples from two different ships (above) and sludge- 
samples taken from these ships (below).