Abstract <p>Procedures for the identification and determination of a number of antioxidant, anticorrosive, and dispersant additives (ionol, diphenylamine, zinc dialkyldithiophosphate, and diester oil) in mineral hydraulic oils were proposed. They included preliminary solid-phase extraction of analytes on a cartridge with hydroxylated silica gel with the subsequent detection by reversed-phase high-performance liquid chromatography. The recovery of analytes was higher than 97%, and the limits of determination and detection of functional additives in mineral hydraulic oil were 0.001 and 0.0006 wt % for ionol, 0.01 and 0.008 wt % for zinc dialkyldithiophosphate, and 0.0005 and 0.00025 wt % for diphenylamine, respectively. It was established that Shell Tellus S2 V 46 mineral hydraulic oil contained 0.16% zinc dialkyldithiophosphate and 0.2% diphenylamine, and Total Hydragri ISO VG 46 contained 0.14% ionol and 0.17% zinc dialkyldithiophosphate. The molecular-weight characteristics of polymer additives to hydraulic oil were determined by gel permeation chromatography, and the concentration of a viscosity additive in a real sample was calculated. The procedures are appropriate for the determination of functional additives and the quality control of mineral hydraulic oil.</p>