We calculate the binding energies of Wannier excitons in quantum well structures consisting of a single slab of GaAs sandwiched between two semi-infinite layers of Al(x)Ga1-xAs as a function of several experimentally adjustable parameters. The exciton Hamiltonian is expressed in the two-band model within the effective mass approximation. The well depth is taken to be finite. A variational method is adopted and a suitable trial wave function with separable form is chosen to solve for the eigenenergies. The binding energies of both the heavy-hole exciton and the light-hole exciton are calculated as a function of the aluminium concentration, band offsets, and the GaAs quantum well width.