Large-pore mesoporous materials were synthesized by incorporating alkanes as swelling agents during micellar solution preparation. The effect of the number of carbon atoms of the alkane on the properties of the final products has been investigated. The optimal swelling effect is obtained with decane, and the largest pore diameter that can be achieved with the latter is 5.0 nm. To further expand the pore size, we have incorporated jointly decane and 1,3,5-trimethylbenzene (TMB). The adding sequence of the two swelling agents has been studied and appears to strongly affect the pore size. This study led us to propose two different mechanisms, describing the swelling effect of decane and TMB molecules, which depend on the preparation conditions.