Shale gas is viewed by many as a global energy game-changer. However, serious concerns exist that shale gas generates more greenhouse gas emissions than does coal. In this work the related published data are reviewed and a reassessment is made. It is shown that the greenhouse gas effect of shale gas is less than that of coal over long term if the higher power generation efficiency of shale gas is taken into account. In short term, the greenhouse gas effect of shale gas can be lowered to the level of that of coal if methane emissions are kept low using existing technologies. Further reducing the greenhouse gas effect of shale gas by storing CO2 in depleted shale gas reservoirs is also discussed, with the conclusion that more CO2 than the equivalent CO2 emitted by the extracted shale gas could be stored in the reservoirs at significantly reduced cost. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.