An effective catalyst includes an amorphous silica-alumina support having a bimodal pore size-distribution. The support may be prepared by a method that includes the physical mixing of two silica-alumina gels prepared so as to have two different average pore sizes. The catalyst has the advantage that both metal dispersion on the support and product diffusion in the pores are optimized. Further, the catalyst has improved performance in the production of hydrocarbons from synthesis gas.