Room-temperature quasi-ballistic electron transport in double-wall carbon nanotubes (DWNT) is demonstrated. Conductance dependence on the length was measured by submerging DWNTs into liquid mercury. The conductance plots show plateaus, indicating weak dependence of the electrode-tube-electrode electrical resistance on the length of the connecting nanotube. We infer a mean free path between 0.6 and 10 mum for similar to80% of the DWNTs, which is in good agreement with calculations based on the electron scattering by acoustic phonons and by disorder. (C) 2004 Elsevier B.V. All rights reserved.