The present study investigated experimentally the effects of various geometric and operating parameters on the mixing characteristics of model liquids undergoing mixing in a novel in-line mixer, viz. an in-line impinging stream (IS) mixer. First, the mixer with one set of three inlet jets was used. Later two sets of inlet jets were used in order to increase the number of impingement zones and hence the mixing capability of the mixer. A statistical analysis was performed to indicate the best geometry of the mixer based on the data of both the mixing effectiveness and the pressure loss due to impingement of liquid streams. (C) 2004 Elsevier Ltd. All rights reserved.