A general, simple and easy to implement analytical model that enables design and analysis of three-fluid heat exchangers with three thermal communications for all flow arrangements is developed. The model is shown to reduce to either a three-fluid, two thermal communications model or the traditional two-fluid heat exchanger model under proper conditions. Six non-dimensional design parameters are identified and their effect on the temperature distributions of the different fluid streams is presented. The model shows that the presence of three coupled thermal interactions makes temperature distributions of the different streams difficult to assess due to slight changes in the design parameters. (C) 2004 Elsevier Ltd. All rights reserved.