We investigate the excitation energy transfer in a guest-host molecular system consisting of a pentacene derivative, namely 6,13-bis(2,6-dimethylphenyl)pentacene (DMPP), doped into tris(8-hydroxyquinolinato)aluminum (Alq(3)) using steady-state and time-resolved photoluminescence (PL) spectroscopy. The concentration dependent energy transfer rate and efficiency are calculated and analyzed in terms of the Forster resonance energy transfer model. A relatively long excitation transfer time (similar to 0.6-3.4 ns depending on the DMPP concentration) and a large transfer radius (31-36 angstrom) are obtained. The Forster radius calculated directly from the Alq(3) PL-DMPP absorption spectral overlap (26 angstrom) is smaller than the transfer radii obtained from the PL studies, which suggests that excitation energy migration within Alq3 plays an important role in the energy transfer process, effectively elongating the transfer radius and increasing the transfer rate and efficiency.