The feasibility and economic worth of the Low Heat Rejection Engine [IHRE] is being studied for applications to the commercial truck market. Different Exhaust Energy Recovery Systems [EERS] have been considered to improve the overall fuel economy of the IHRE. This paper reports on a performance assessment study of likely IHRE-EERS combinations. The study used a partial factorial orthogonal scheme and Detroit Diesel Allison's engine simulation programs as the basis for the statistical parametric optimization. Emission constraints were also imposed.Optimum fuel economy at various IHR levels is predicted. Quantitative sensitivities of the bsfc and other variables to major influential parameters have been determined. Engine sizing for future on-highway truck market is proposed.