Abstract: Charging gases from each coking chamber in a battery of coke ovens are withdrawn through a closable ascension pipe into only a first gas main. The gases liberated during carbonization of the coal charge in each oven chamber are withdrawn through a closable ascension pipe into only a second gas main throughout the remainder of the carbonization process. The gases in each gas main are sprayed with flushing liquor. Gases are continuously transferred from the second gas main through pipes into the first gas main to equalize the gas pressure within the gas mains. Flushing liquor removed from the first gas main is processed to remove the tar content therefrom and to provide a clear flushing liquor which is used to spray charging gases within the first gas main.