Another method of producing formaldehyde is through the oxidation of hydrocarbon gases. An increase in the amount produced of formaldehyde is expected in this process. However, the hydrocarbon formaldehyde is usually obtained as dilute solution which is not economically concentrated accompanied by other aldehydes and by-products. However, improvements have been effected by the use of special catalysts and better methods of control. Wheeler demonstrated that methane is not oxidized at an appreciable rate below 600°C. The difficulty in this method is in controlling the oxidation of reaction. Ethylene, ethane and propane oxidations can be controlled to yield formaldehyde under similar conditions to methane. Higher hydrocarbon gases can be oxidized at much lower temperatures than methane and ethane. These methods have been described by Bibb also reported by Wiezevich and Frolich, who used iron, nickel, aluminum, and other metals as catalysts and employed pressures up to 135 atmospheres. The Cities Service Oil Company has developed a commercial process using this method