The paper presents a pioneering attempt in the last 35 years, to summarize the accumulated data on geochemistry of water-dissolved gases of oil and gas-bearing deposits in northern and arctic regions of Western Siberia. Water- dissolved gases from all the studied oil/gas fields are characterized by absolute predominance (up to 75-99 vol.%) of the methane series hydrocarbons in their composition. The identified (after the L.M. Zorkin's classification) four classes of hydrocarbon type of water-dissolved gases (vol.%) are designated as: dry (ΣHH < 1), lean (Σ?HH = 1-3), semi-fat (ΣHH = 3-5) and fat (ΣHH= 5). The total gas saturation of groundwaters ranges from 0.3 to 5.7 L/L with CH4 concentrations averaging 95.5 vol.% in the Aptian-Albian-Cenomanian to 83.3 vol.% in the Lower-Middle Jurassic complexes. The levels of homologues ΣHH (C2H6, C3H8, C4H10, C5H12 and C6H14) tend to increase with depth: from 1.34 vol.% in the Aptian-Albian-Cenomanian to 11.67 vol.% in the Lower-Middle Jurassic complex. The maximum ΣHH concentrations reaching 30 vol.% were found at the Neocomian base in the peripheral waters of oil accumulations. CO2 levels show an increasing trend with depth, whereas N2 concentrations tend to decrease. Given the increased depths and more severe temperature conditions, the level of hydrocarbon generation remains high, however hydrocarbon series is characterized by a shift towards liquid components and methane homologues (the main zone of oil /fat gases generation). Therefore, the revealed in the Lower-Middle Jurassic complex highly gas-saturated groundwaters (up to 4.5-5.7 L/L) enriched with methane homologues allow to assess their hydrocarbon prospects as very high.