Lately, the selection and research of the isolated core from argillaceous-siliceous deposits of the Bazhenov formation allowed receiving new information about reservoirs of these strata. New information contradicts the earlier existing opinion, about clay reservoirs of the Bazhenov formation. On the example of a several fields, located on the different flanks of the Frolovsky megahollow in Western Siberia, it was proven that generally, the reservoirs of the Bazhenov formation are dated for radiolarian layers, in various degree siliceous or carbonaceous.