Basin and petroleum system modeling requires reliable input data on the formation thermal properties and heat flow. It was established from analysis that previous traditional experimental methods and theoretical models could not provide satisfactory quality of the thermal property data for sedimentary rocks. This is a reason that the input thermal property data recommended in basin simulators have essential uncertainties and errors (up to 50-80%). Additionally, it was established from geothermal experiments in deep scientific drilling programs that previous estimates of heat flow from the measurements in shallow wells have given heat flow by 40-130% lower compared to terrestrial heat flow inferred from recent geothermal experiments in super-deep and deep scientific wells. Sensitivity study analysis for a basin model of a section of the West Siberia platform, when the basin modeling results obtained with the default data and vast experimental data on thermal properties and heat flow were compared, demonstrated very serious errors in the basin modeling results caused by default data application. The new experimental technique for high precision measurements of the rock thermal properties on cores and a new approach to heat flow determination accounting for its vertical variations are suggested to improve the basin modeling reliability essentially.