We report high-power, dual-wavelength tunable operation of an Er:Yb co-doped fiber laser using two volume Bragg gratings arranged in parallel. The wavelength separation for the two operating wavelengths was continuously tuned from 0.3 to 29.2nm (0.04 to 3.7 THz) with a total output power of >13Wfor a wavelength splitting range of <20 nm. A maximum output power of 17.9W was obtained at a wavelength separation of 0.3nm for a launched pump power of 65.3W, which corresponds to a slope efficiency of 28.6% with respect to the launched pump power.