This paper presents a novel heuristic optimization approach to constrained economic load dispatch (ELD) problems using the adaptive-variable population - PSO technique. The proposed methodology easily takes care of different constraints like transmission losses, dynamic operation constraints (ramp rate limits) and prohibited operating zones and also accounts for non-smoothness of cost functions arising due to the use of multiple fuels. Simulations were performed over various systems with different numbers of generating units, and comparisons are performed with other existing relevant approaches. The findings affirmed the robustness, fast convergence and proficiency of the proposed methodology over other existing techniques. (C) 2008 Elsevier Ltd. All rights reserved.