This paper assesses the issue of monitoring to measure potential emissions from leakage at geologic sequestration (GS) sites for purposes of greenhouse gas (GHG) accounting under an emission reduction program. We find that a GHG accounting program can reasonably assume that there is no atmospheric leakage from GS sites as long as routine subsurface monitoring shows no loss of containment. If loss of containment is detected, current monitoring technology, such as hyperspectral imaging, should be able to detect and locate leakage at levels of concern at some but not all sites. If leakage can be detected, then it can be reliably quantified using existing technology. The disparities in leakage detection capability produced by geologic and ecosystem variations require a flexible GHG accounting policy for GS sites during the operations phase. The potential for leakage emissions during long-term stewardship is low, but mechanisms to account for it, such as an emissions reserve program, are important for building public support for CCS technology and supporting national emission reduction goals.