A method for producing C 2+ hydrocarbons and hydrogen comprising: (a) introducing a reactant mixture to a reactor, wherein the reactant mixture comprises methane (CH 4), and wherein the reactor comprises a preheat zone, a primary reaction zone, a secondary reaction zone, and a quench zone; (b) heating the reactant mixture to a preheating temperature in the preheat zone to yield a heated reactant mixture; (c) generating free radicals in at least a portion of the heated reactant mixture in the primary reaction zone to form a primary effluent mixture comprising free radicals, C 2+ hydrocarbons, hydrogen, and unreacted methane; (d) reacting at least a portion of the primary effluent mixture in the secondary reaction zone to form a secondary effluent mixture comprising C 2+ hydrocarbons, hydrogen, free radicals, and unreacted methane, wherein the secondary reaction zone is characterized by a secondary reaction zone temperature, wherein the secondary reaction zone temperature is greater than the preheating temperature, wherein an amount of unreacted methane in the primary effluent mixture is greater than an amount of unreacted methane in the secondary effluent mixture, and wherein an amount of free radicals in the primary effluent mixture is greater than an amount of free radicals in the secondary effluent mixture; (e) cooling at least a portion of the secondary effluent mixture in the quench zone to a quench temperature to yield a product mixture comprising C 2+ hydrocarbons, hydrogen and unreacted methane, wherein the quench temperature is lower than the secondary reaction zone temperature; and (f) recovering at least a portion of the product mixture from the reactor. (a) introducing a reactant mixture to a reactor, wherein the reactant mixture comprises methane (CH 4), and wherein the reactor comprises a preheat zone, a primary reaction zone, a secondary reaction zone, and a quench zone; (b) heating the reactant mixture to a preheating temperature in the preheat zone to yield a heated reactant mixture; (c) generating free radicals in at least a portion of the heated reactant mixture in the primary reaction zone to form a primary effluent mixture comprising free radicals, C 2+ hydrocarbons, hydrogen, and unreacted methane; (d) reacting at least a portion of the primary effluent mixture in the secondary reaction zone to form a secondary effluent mixture comprising C 2+ hydrocarbons, hydrogen, free radicals, and unreacted methane, wherein the secondary reaction zone is characterized by a secondary reaction zone temperature, wherein the secondary reaction zone temperature is greater than the preheating temperature, wherein an amount of unreacted methane in the primary effluent mixture is greater than an amount of unreacted methane in the secondary effluent mixture, and wherein an amount of free radicals in the primary effluent mixture is greater than an amount of free radicals in the secondary effluent mixture; (e) cooling at least a portion of the secondary effluent mixture in the quench zone to a quench temperature to yield a product mixture comprising C 2+ hydrocarbons, hydrogen and unreacted methane, wherein the quench temperature is lower than the secondary reaction zone temperature; and (f) recovering at least a portion of the product mixture from the reactor.