Using the data for the oil fields of the Southern Caspian (Azerbaijan, Western Turkmenistan, Georgia) and Northern Caucasian Mangyshlak (Ciscaucasia) oil-and-gas bearing basins (OGB) as an example, the investigational results for immature oils and condensates generated by the organic matter (OM) of both shallow marine and coastal-deltaic facies have been summarized. The physicochemical properties and the hydrocarbon and trace-element compositions of oils and condensates have been considered and their key features have been revealed. It has been shown that these oil and condensate parameters are related to the composition of the source OM and the multistage character of its transformation. In other words, the whole variety of geological processes pertaining to the burial and transformation of the original, oil-generating source OM is reflected in the geochemical features of oils and condensates, thereby giving another important and convincing piece of evidence for the organic origin of oil.