The invention relates to a process for converting hydrocarbon inputs by thermal steamcracking to give at least one olefin-containing product stream comprising at least ethylene and propylene, by at least partly converting a hydrocarbon input in at least one cracking furnace (2), wherein the hydrocarbon input is converted under mild cracking conditions in the cracking furnace (2), mild cracking conditions meaning that propylene to ethylene are present in a ratio of 0.81 to 1.6 kg/kg at the cracking furnace exit, and the hydrocarbon input comprising predominantly hydrocarbons having a maximum carbon number of 6, preferably a maximum of 5.