There are several recent reports of the occurrence, in a variety of marine surface sedi- ments of a C20 highly branched alkane and related compounds l-3. The electron impact spectrum (EI) of the alkane is unusual in that it is characterised by the presence of pairs of ions at m/z 168/169 (ca. lo%, 5% respectively), m/z 196/197 (0.8 : 1; m/z 197 < 1%) and m/z 210/211 (0.7 : 1; m/y211 < l%)2s3. The compound is the second most abundant component of the ...