—We present research results for the geologic structure of the De Long, Aion, and Pegtymel sedimentary basins of the East Siberian Sea. The materials of geological surveys and drilling in their land area and island surroundings, the data obtained from geophysical surveys conducted by Dal’morneftegeofizika, MAGE, and Sevmorgeologiya, and the seismic and deep-drilling data on the U.S. sector of the Chukchi Sea are summarized and analyzed. Pre-Paleozoic strata and the sedimentary cover have been identified throughout the sections of the sedimentary basins, which suggests the existence of a geologic “cover–basement” boundary rather than an arbitrary called “acoustic basement” horizon. The data on the geologic structure and gas saturation of the upper parts of the sedimentary sections were obtained during the study and gas-geochemical testing of core samples and bottom sediments from coastal shallow wells and corers. Gas contained in the rocks and bottom sediments in the study area includes hydrocarbon gases (HCGs) (СН4, С2–С5, and their unsaturated homologues), СО2, Н2, Не, N2, Ar, and, seldom, CO and H2S. The data on gas saturation of bottom sediments and the geochemical parameters of their syngenetic and epigenetic gases are presented. Areas of abnormal saturation of sediments with CO2, СН4, other HCGs, H2, and He (>5, 0.05, 0.001, 0.005, and 0.005 cm3/kg, respectively) have been identified, and maps of the gas saturation patterns in bottom sediments have been compiled. It is established that both gas saturation and distribution are determined mainly by the geologic evolution, tectonics, magmatism, geocryologic conditions, lithologic composition, catagenesis, coal content, bituminosity of sedimentary rocks, and oil and gas potential of the study area.