This paper presents a rigorous investigation for efficiency, thrust, and fuel consumption optimization of a subsonic/sonic turbojet engine. A thermal model of the turbojet engine is developed for optimization investigation. A many-objective optimization problem is formed by considering maximization of thermal efficiency, propulsive efficiency, specific thrust and minimization of thrust-specific fuel consumption of turbojet engine and solved using multi-objective heat transfer search (MOHTS) algorithm. Results are obtained as a set of Pareto-optimal points for the many-objective problem. Comparative results of many objective and multi-objective optimization are presented on the two-dimension objective space. Design points having 70.95% thermal efficiency, 60.23% propulsive efficiency, 0.0162 kg/s/kN specific fuel consumption, and 1.1666 kN/kg/s specific thrust are obtained during the optimization. Decision-making approaches like LINMAP, TOPSIS, and fuzzy are used to select the final optimal solution from the Pareto optimal set of the many-objective optimization. Finally, to reveal the level of conflict between these objectives, the distribution of each operating variables in their allowable range is also shown in two-dimension objective spaces. (C) 2017 Elsevier Ltd. All rights reserved.