Abstract: Any kind of virgin, low-sulfur crude oil is directly treated in a two-stage delayed coking process for yielding non-crystalline coke in the first stage and high-crystalline coke in the second stage, which process comprises preheating the crude oil in a tube heater to 460.degree. - 520.degree.C under 5-20 kg/cm.sup.2 G, maintaining the oil therein at that temperature for 30 - 500 seconds to allow the oil to be heat-soaked, subjecting the oil to first delayed coking under relatively mild conditions and subjecting the uncoked heavy residual oil to second delayed coking under relatively severe conditions.