Surgical resection of the epileptogenic zone (EZ) is the only effective treatment for many drug-resistant epilepsy patients, however the pre-surgical identification of the EZ is very challenging. Unfortunately, it is not possible to precisely define the EZ in practice because the EZ does not have a clear biomarker. For a long time in a history of electroencephalography, sharp, rapid spikes of high amplitude during the ictal period (also occurring interictally) were considered as an epileptiform activity, which indicates the seizure onset zone and was recommended for resection. Recently, high‑frequency oscillations (HFO) have been considered as pathological phenomena correlated with seizure onset zone with higher reliability than interictal spikes and MRI structural lesions. However, oscillations in the frequency range of HFO can also be recorded from normal, non‑pathological tissue. To separate the seizure onset zone from the non-pathological area, we proposed a measure of the strength of coupling of high‑frequency oscillations with low‑frequency activity during seizure onset. All these biomarkers will be discussed and compared with respect to the surgical benefit of patients’ outcome.