We studied the electrocapillary curves (ECC) sigma(phi) of pure copper and copper doped with 0.05 mass% of sulfur at 1200 degrees C in contact with boron + aluminium oxide electrolyte. A novel approach of the ECC determination involving in turn measurements of interfacial tension sigma by capillary depression (CD), maximum pressure (MP) in a drop and X-ray survey of sessile drop (SD) methods was used. The highest accuracy was shown by the CD method, which was used in oxide systems for the first time.