Currently, Colombia is starting several studies for the development in unconventional hydrocarbon reservoirs, however, radioactive analysis for this area have never been developed. In fact, during more 50 years of oil and gas operations, these kinds of studies have not been developed. For this reason, eight rock samples coming from oilfields from the Middle Magdalena Valley Basin by using gamma and alpha spectrometry were analyzed to quantify natural radionuclides from both 238U and 232Th series. The results were supported with multielement and mineralogical data obtained by ICP-MS and XRD techniques. Activity concentrations of natural radionuclides from both series 238U and 232Th showed secular equilibrium, in an average between 60 and 180 Bq kg-1, respectively, excepting for two wells that had higher values (450 – 600 Bq kg-1). Additionally, 40K was also measured in all samples indicating values from 180 to 350 Bq kg-1. On the other hand, the multielement composition results presented a high variability: V (500 - >1000 ppm), Zn (360 – 3300 ppm), Ni (130 – 1440 ppm) y Cu (50 – 110 ppm) and mineralogical analysis allowed to observe minerals such as: Quartz, kaolinite, pyrite, calcite, illite, and gypsum in different percentages. In general, the activity concentrations of the studied natural radionuclides were highly related to the chemical composition of the rocks, ratifying their different sources.