26 
Fig. 22: Mass chromatograms of masses 191 and 217 of two different FIFOs (same samples as 
in Fig. 21). 
Crude oils subjected to weathering may, therefore, show a similar composition as HFOs 
which do not contain any cracking residues. It may be hardly possible, therefore, to 
differentiate between a HFO which does not contain such cracking residues and a weathered 
crude oil. The HFO sample shown in Figure 21 on the left side can be easily mistaken for a 
weathered Russian crude oil (Fig. 23).