This paper reports the results of a study on mixing by an impeller and a jet in the 19,000 m(3) crude oil storage tank of the Kermanshah Refinery of Iran. A three-dimensional modeling was carried out using an in-house computational fluid dynamics (CFD) code. The jet was placed theoretically next to the impeller and its effect on reducing the mixing time was investigated. Various jet outflow rates including: 33, 66, 132 and 264 m(3) h(-1) were examined and the effect of the angle between the jet and the impeller on the mixing time for four setups was investigated. The results show when the angle between the jet and the impeller are 15 degrees and 60 degrees, the homogenization time is lower than that of other layouts. In addition, the homogenization progress by the selected jet-impeller layout was compared with the multiple-impellers setups. The results showed that a simple jet-impeller system operates in a more efficient way than even five-impeller setup. (C) 2006 Elsevier Ltd. All rights reserved.