The invention relates to both a method and apparatus for thermal cracking hydrocarbons. The apparatus includes a rotating conical drum assembly within a vessel containing a hydrocarbon feedstock. The conical drum assembly is internally heated to cause cracking of hydrocarbons adjacent the conical drum surface and the formation of coke on its external surface as the conical drum rotates. Coke is removed from the drum surface by a coke removal system and cracked hydrocarbon product is collected as a vapor.