The on-stream time of cracking furnaces is limited by the formation of coke on the internal skin of the reactor tubes. Rigorous simulations of an ethane cracking furnace, coupling reactor and furnace models with the kinetics of coke formation prove that the run length of the furnace can be augmented by more than 40% by replacing the cracking tubes of circular cross section by cracking tubes of elliptical cross section. The increase of furnace heat-transfer efficiency and the more uniform circumferential heat fluxes and temperatures favor the run length of the furnace with tubes of elliptical cross section.