Current estimates indicate a significant anthropogenic emission of methane from animal waste. However, these are quite uncertain because they were derived using limited experimental data. Year-round measurements of methane and nitrous oxide fluxes from liquid swine manure storage systems were initiated in 2000, using a micrometeorological mass balance method (MBM). Four masts surrounding a storage tank, with four air sampling intakes each were used. Half-hourly concentrations of N2O and CH4 in air samples were determined using two tunable diode laser trace gas analyzers housed in a mobile trailer that was moved to various locations over the year. Wind speed was monitored at four heights using cup anemometers. Detailed wind direction measurements were carried out in order to determine the air’s travel path over the emitting surface. Typical methane and nitrous oxide fluxes measured during the year will be presented. The effect of environmental conditions (eg. temperature), and manure characteristics (eg. chemical composition, redox potential) will be discussed.