The three-dimensional flow and mixing characteristics of multiple and multi-set three-dimensional confined turbulent round opposing jets in a novel in-line mixer were examined numerically using the standard k-epsilon turbulence model. The model was validated with the available experimental results in a Tee mixer [D.Y. Tang, A.J. Dukat, J.J. Ou, Dynamics of fluid mixing induced at a T-junction, experimental characterization and fluid dynamic computation of temperature distribution in space, Ind. Eng. Chem. Res. 32 (1993) 1727-1733] in which a side stream normally impinges a main stream. Good agreement between the simulated and experimental results is obtained. The effects of multiple opposing jet injection and multi-set opposing jet injections with/without offset on mixing are discussed for this novel opposing jet configuration. (c) 2006 Elsevier B.V. All rights reserved.