Deeply refined petroleum oils containing additives for increasing cooling speed, thermal and thermo-oxidative stability. They have high inflammation point and fire point, small evaporation capacity and very low tendency to create sludge. They guarantee even through-quenching of quenched components. Oils QUE 46 and QUE 68 are also designed for use as heat transferring media for heating of heating system up to 315 °C in closed systems and 230 °C in opened systems.