  We present detailed estimates of ''type-I'' migration rates for low-mass
proto-planets embedded in steady-state T-Tauri alpha-disks, based on Lindblad
torque calculations ignoring feedback on the disk. Differences in migration
rates for several plausible background disk models are explored and we contrast
results obtained using the standard two dimensional formalism of spiral density
wave theory with those obtained from a simple treatment of three-dimensional
effects. Opacity transitions in the disk result in sudden radial variations of
the migration rates. Regions with minimal migration rates may be preferred
sites of gravitational interactions between proto-planets. Three-dimensional
torques are significantly weaker than two-dimensional ones and they are
sensitive to the surface density profile of the background disk. We find that
migration times in excess of runaway envelope accretion times or T-Tauri disk
lifetimes are possible for Earth-mass proto-planets in some background disk
models, even at sub-AU distances. We conclude that an understanding of the
background disk structure and ''viscosity'', as well as a proper treatment of
three-dimensional effects in torque calculations, are necessary to obtain
reliable estimates of ``type-I'' migration rates.
