The Birkeland–Eyde process is relatively inefficient in terms of energy consumption. Therefore, in the 1910s and 1920s, it was gradually replaced in Norway by a combination of the Haber process and the Ostwald process. The Haber process produces ammonia (NH3) from molecular nitrogen (N2) and hydrogen (H2), the latter usually but not necessarily produced by steam reforming methane (CH4) gas in current practice.