The effects of jet angle and elevation on mixing in a fluid jet agitated tank were investigated using computational fluid dynamics (CFD). Results show that, for a given geometric arrangement, the angle of the jet injection is significantly more important in determining the time required for 95% mixing than the length of the jet. For an aspect ratio of I and for a side jet injected at the bottom of a tank, the longest jet length, corresponding to an angle of injection of 45degrees, does not give the shortest time as suggested by many previous workers but one of the longest mixing times. An angle of injection of 30degrees gives the shortest mixing time. Results also show that the mixing time does not change monotonically with the angle of injection or with the level at which the jet is injected. This means that when designing a jet mixer, careful consideration should be given to the angle as well as the location of the jet. Results also show that a significant reduction in the mixing time is possible if two side jets are used instead of one. The improvement is between 40% and 68% for jet Reynolds numbers between 3000 and 7000. (C) 2003 Elsevier Ltd. All rights reserved.