The mineralisation of organic matter (OM) when sewage sludge was used as amendment in 70 contrasting agricultural soils from Spain was analysed. Soils received a single dose of sewage sludge (equivalent to 50t dry weight ha-1) and the O2 consumption was continuously monitored for 30 days using a multiple sensor respirometer in a laboratory experiment. The cumulative O2 consumption and rates after 8 and 30 days of incubation (O2 cum 8d, 30d and O2 rate 8d, 30d), the respiratory quotient (RQ), the maximum O2 rates over the incubation period (O2 max) and time from the beginning of the incubation when O2 max occurred (Tmax), were determined in both amended and non-amended soils. Sewage sludge application resulted in increased values for O2 max, O2 rate 8d, and O2 cum 30d. Differences were minor for Tmax, RQ 8d and O2 rate 30d. A considerable amount of the initial OM applied was mineralised during the first 8 days. Organic matter decomposition (as expressed by O2 cum 30d) was favoured in soils with high values of pH, carbonates, soil organic carbon and low values of amorphous Mn. Soils with these characteristics may potentially lose soil C after sewage sludge application.