We discuss the results of measurements of the thermal conductivity of the Bazhenovo Formation rocks from wells drilled in the Salym petroliferous area of the West Siberian Plate. The thermal conductivity was measured by “Thermal-conductivity comparator” and “Scanning thermal-conductivity meter” in different years. A total of 225 measurements were made in two directions with respect to the rock layering: parallel (λ1) and orthogonal (λ2). The results show that the Bazhenovo Formation rocks are mostly of abnormally low thermal conductivity: λ1 = 1.0–2.3 W/(m⋅K) (average is 1.6 W/(m⋅K)) and λ2 = 0.8–1.9 W/(m⋅K) (average is 1.3 W/(m⋅K)). This leads to an abnormal increase in geothermal gradient within the Bazhenovo Formation. Such geothermal-gradient anomalies can be easily revealed by high-precision thermal logging. It is also shown that the thermal conductivity of the studied rocks is in inverse relationship with their organic-matter content.