The efficiency of a bank of dense medium cyclones treating medium coking coal in the size range of - 13 + 0.5 mm. was evaluated. Performance indicators for evaluating the efficiency of the separation were identified. Various variables affecting the efficiency of the dense medium cyclones (DMC) were examined to identify those that affect the DMC operation and new levels of the parameters identified to bridge the gap between the actual and the ideal. The studies showed that for coals having a high level of NGM, feed rate could be one of the critical parameters affecting the efficiency of separation. Feed rate and the spigot diameter were used to reduce the EP and for coarser adjustments of cutpoints. Mathematical model for the cyclones was developed using the generalised distribution curve, represented by the equation of the form: y = 100[exp - (x - x(0))(a)/b] where y is the percent distribution of clean coal corresponding to a reduced specific gravity x, x is defined as Sg/Sg(50), and a, b and x(0) are constants. Corelations were then developed relating the coefficient of separation (showing the separation efficiency) and the EP to the design and operating variables of the cyclones.