Organosulfonic acid mesoporous silicas further functionalized with hydrophobic organic groups were synthesized via postsynthesis grafting and one-step co-condensation methods. The resulting materials were tested in the esterification of fatty acid with methanol to produce methyl esters as a pretreatment step in the production of biodiesel. Incorporation of the hydrophobic group into the organic-inorganic hybrid acid catalyst was found to improve the performance of the resulting catalyst. However, the performance of the multifunctionalized mesoporous materials demonstrated a strong dependence on the incorporation method and on the size of the hydrophobic organic groups. Solution effects within the reaction mixture appeared to influence the catalytic activity of the catalysts. The results indicate the potential for intentional design of the catalytic environment at a molecular level with the use of organic-inorganic mesoporous materials. (C) 2004 Elsevier Inc. All rights reserved.