Viscous gas flows above linearly shrinking and stretching sheets with mass transfer are studied via theoretical analysis. Effect of mass-transfer induced slip at a moving surface on gas flows, which has not been considered in all previous studies, is systematically investigated. Net mass-transfer on a moving surface is demonstrated by a newly developed slip flow model (Wu, 2014) to introduce a gas slip velocity component in addition to the slip velocity component due to velocity shearing considered in the original 1st or 2nd order slip flow models. Our results show that mass suction induces a slip velocity against the sheet motion. The competition between flow driven effects of mass-suction induced slip and sheet motion significantly expands the available solution space, and adds to the solution space one more solution sub-region, which is absent when mass-suction induced slip is not considered. Mass-suction induced slip may even achieve a dominant flow driven role by totally reversing the flow direction of adjacent gases to flow against the sheet motion. Mass-injection induced slip enhances the flow driven effect of the moving sheet. (C) 2015 Elsevier Ltd. All rights reserved.