Using measurements of methane isotopes in ambient air and a 3D atmospheric transport model, in Krakow, Poland, we mainly detected fossil-fuel-related sources, coming from coal mining in Silesia and from the use of natural gas in the city. Emission inventories report large emissions from coal mine activity in Silesia, which is in agreement with our measurements. However, methane sources in the urban area of Krakow related to the use of fossil fuels might be underestimated in the inventories.