A 4-day continuous reaction could be established for a reactor containing CH4/O2 (2:1, 35 mL, 0.1 MPa) with 0.24 mol% NaNO2 (2.3 μmol) in HCl/HTFA solution. To keep the reaction system stable, the external CH4/O2 (2:1, 0.1 MPa) was added into the reactor every 24 hours. The initial gas in the reactor may be as the buffer gas, and the external gas added is called the input gas here. When the selectivity of MTFA and CH3Cl is very high (over 90%), the ratio of CH4/O2 consumed is very close to 2:1. Thus, at the end of the continuous reactions, the amount of the input gas could be equal to that of the consumed gas during the reaction. Based on the input CH4/O2 (2:1, 21 mL, 0.1 MPa), the yield of MTFA was 85% with the selectivity of 90% in the 4-day continuous reaction. It was proved that the ratio of CH4/O2 (1:1~4:1) in the buffer gas and the amount of the input gas (15~30 mL) did not greatly affect the MTFA production and selectivity with the TOFs close to 2.2 mol MTFA mol NaNO 2 -1 h -1 (Figure , Table ). However, in a 7-day continuous reaction, the external HCl (12 M) was also necessary to be added in several times with the input gas, which could effectively maintain the TOF at 2.5 mol MTFA mol NaNO 2 -1 h -1 (Table ). One of reasons is that a lot of MTFA accumulated in the solution can block the reaction, but more HCl (12 M) added will overcome this problem partially (Table ). In this reaction, the yield of MTFA was 88.6% based on the input CH4/O2 (2:1, 42 mL, 0.1 MPa) or 48.3% based on all CH4/O2 (2:1, 77 mL, 0.1 MPa) with a concentration of MTFA of ~510 mmol L -1 in the resultant solution. In other continuous experiments for 2, 3 and 4 days, both the methane conversion and the MTFA selectivity were over 90% based on the input CH4/O2 (2:1), and the TOFs were 2.2~2.3 mol MTFA mol NaNO 2 -1 h -1 (Figure , Table ). Meanwhile, the ratio of CH4/O2 in the reactors was always around 2:1 as the initial state. It indicates that the aerobic oxidations of methane can proceed very well to produce methyl ester in an excellent selectivity under the stable conditions, including temperature, light, pressure, acidity, and the ratio of CH4/O2, et al.