The interdependence of phytane and isoprenoids containing less than 20 carbons is considered in this study. The relationships of pristane to phytane, and pristane and phytane to lower molecular weight isoprenoids, are linear. The lines of best fit commonly possess a positive intercept on the dependent variable axes (pristane and lower molecular weight isoprenoids). The positive y-axis intercept suggests that a fraction of pristane and a fraction of lower molecular weight isoprenoids cannot be attributed to chlorophyll (phytol) diagenesis. This observation supports the conclusion that some amount of the nonphytane isoprenoid assemblage must be attributed to a higher molecular weight "parent" compound(s) whose identity can only be suggested. Isoprenoid ratios and distributions have been useful in geochemical correlations (oil-oil). However, the correlation value of these hydrocarbons should be viewed critically because of the "partial" interdependence of phytane and lower molecular weight isoprenoids.--Modified journal abstract.