Abstract We report the results of a first attempt to monitor the gas emission from two distinct vents of two mud volcanoes in Azerbaijan, representing in both cases a fraction of the total amount of gas emitted by these structures. One monitoring station was placed on a salse lake in the crater area of the Dashgil mud volcano. It recorded methane flux from December 2003 to March 2006 and additionally radon emission in 2004. The second monitoring station was placed in October 2004 on the Perikushkul mud volcano. Both vents show significant variations in gas output with time. Month-long phases of near-constant gas output and periods characterized by large-scale daily variations were both observed. We proposed that fluctuations in gas output are connected with short-term variations in vent geometry (Dashgil) or with periodic buildups of methane at depth and sudden discharges (Perikushkul). Methane emission from the vent at Dashgil shows a well-developed periodicity of 24.05 hr, whereas no periodicity at Perikushkul was observed. During the observational period, both vents exhibited slowly decreasing gas output with time.