“…Trace element abundances in oil, particularly Ni, V and Mo, are often present at the parts per million (ppm) level, (Curiale, 1987;Manning and Gize, 1993) and are known to exist as part of a porphyrin structure, as a tetrapyrrole complex (Filby and Van Berkel, 1987;Manning and Gize, 1993). In addition to these trace elements, rhenium (Re) and osmium (Os) have been reported to occur in oil, with abundances one to two orders of magnitude lower than Ni, V and Mo (parts [weight] per billion/trillion, [ppb/ppt]), respectively (Poplavko et al, 1975;Barre et al, 1995;Woodland et al, 2001;Selby and Creaser, 2005a,b;Selby et al, 2005).…”