The continuous-phase-mixing characteristics of a sieve-tray extractor were studied in a specially designed single-stage experimental apparatus. Two chemical systems were studied: toluene-water and n-butanol-water, The degree of continuous-phase axial mixing was determined for various tray geometries and phase now rates. A predictive model was developed and combined with a point efficiency correlation to yield an overall tray efficiency. The results indicate that the level of continuous-phase mixing does not significantly affect the overall mass-transfer efficiency of an extractor sieve tray.