This paper evaluates the performance of horizontal pneumatic conveying under different gravity environments. An Euler-Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux and mean conveying velocity in Lunar and micro-gravity conditions. Gravity reduced computations predict an increase of particle-wall collisions with the upper wall of the channel affecting greatly the particle mass flux profile in the case of low wall roughness and small particle mass loading. If gravitational settling is reduced, e.g. by means of higher wall roughness and/or higher particle mass loadings, particle mean conveying velocity is very similar in Earth and micro-gravity conditions.