Here, we reported on experimental studies related to the exposure of oil to a 50 Hz electromagnetic field (0.81 T strength) and examined the changes in the geochemical characteristics of oil: n-alkane distribution, isotopic composition (δ13C), and concentration of paramagnetic centers. We discovered that electromagnetic fields have impacts on the distribution of n-alkanes and on their individual isotopic composition, with the concentration of paramagnetic centers remaining unchanged. While discussing the results, we looked into the state-of-the-art of research on electromagnetic exposures of the bottom-hole formation zone and into natural electric and geomagnetic fields. We consequently hypothesized that natural geomagnetic fields can influence the geochemical evolution processes of oil. This hypothesis requires further studies to reveal the frequency and strength characteristics of natural geomagnetic fields.