Abstract: Based on the steric effect,ligand packing around the uranyl equatorial plane should be neither overcowded nor undercrowded. The sum of Ligand's Fan Angle(FAS)around the uranyl equatorial plane provides a useful criterion for estimating steric crowding.FAS of UO₂(OAc)Br(TBP)₂ is 180°indecating the most favorable packing. It is therefore expected that a higher extraction efficiency should coincide with the formation of the more stable complex. The above speculation was confirmed by extraction of uranyl ion in the substrates of sodium acetate-acetic acid and sodium bromide. Keeping the total concentration of substractes constant, synergistic extraction is found at l:10 acetate to bromide ratio. The extracted complex was proved to be UO₂(OAc)Br(TBP)₂ by using the slope method.