The present work proposes two methodologies for the optimization of a Type III pressure vessel: genetic algorithms and simulated annealing. The vessel is considered to have a capacity of 10 L, a working pressure of 70 MPa and a safety factor of 2.35. An objective function is proposed based on design variables (composite thicknesses) and two penalty factors that evaluate the performance of the liner and the composite material. Numerical analysis shows that the proposed methodologies produce more efficient designs, reducing weight between 5.7% and 7.1% vs. previously published results. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.