We analyze the doping dependence of the thermopower and conductivity of ropes of single wall carbon nanotubes using a tight binding model. A sizeable value of the Seebeck coefficient in these systems together with its Fermi liquid like temperature behavior indicate an asymmetry near the Fermi surface. We discuss two possible explanations for this asymmetry of the electronic structure of the nanotube ropes, one due to defect states, another resulting from the intertube interactions.

PACS numbers: 73.20.Dx, 72.80.Rj, 85.30.Vw