Interesting performance indices for a decanter centrifuge used in oil extraction from olive paste were found through an empirical black box approach to oil extraction using a decanter centrifuge validated with experimental data. The performance indices identified were: oil recovery efficiency, the separation coefficient and husk water content. Two decanter centrifuges were compared and based on our experimental data we identified an empirical model of the decanter centrifuge suitable for use both as a comparison between two or more machines and as automatic control of the machine in order to adapt it to the olive paste. The average RMSEP% when forecasting the mass flow rate of the outgoing oil was 4.4% for decanter A and 4.3% for decanter B. When using the empirical model to measure oil recovery efficiency against the mass flow rate of the olive paste, on varying the paste dilution, there is an "indifference point" where the oil recovery efficiency is invariant with respect to the dilution coefficient of the olive paste. Both the oil recovery efficiency and the mass flow rate of the olive paste at this point are two fundamental performance factors that allow two or more decanter centrifuges to be compared. (C) 2009 Elsevier Ltd. All rights reserved.