The composition and distribution of terpanes in oil shows that emerge from the bottom of Lake Baikal were studied. The oil samples from three sites of Baikal showed different extents of their bacterial degradation, from practically unaltered to heavily degraded oils. In the unaltered samples of oils and moderately degraded differences, a unique variety of biomarkers (sesquiterpanes, secohopanes, new regular hopanes with still unknown structure, oleonane, -carotane, etc.) was discovered. It was shown that the concentration of triterpanes and -carotane increases with a growth in the degree of bacterial degradation and the amount of alkanes and sesquiterpanes is simultaneously reduced. The array of the obtained data suggests that the source of Baikal oils is the organic matter buried in freshwater reservoirs. In this organic material, together with the remnants of the living matter of lacustrine organisms, a significant role was played by the remnants of higher plants brought from the land. The age of source rock cannot be older than the Cretaceous, i.e., the time of appearance of angiospermous plants on the land (presence of oleanane).
