The capture of data provenance is a fundamentally important task in eScience. While provenance can be captured using techniques such as scientific workflows, typically these techniques do not trace internal data manipulations that occur within off-the-shelf analysis tools. Yet it is still essential to capture data provenance within such environments. This paper discusses an in situ provenance approach for spreadsheet data in MS Excel, a commonly used analysis environment among scientists. We describe the design and implementation of an Excel tool that captures provenance unobtrusively in the background, allows for user annotations, provides undo/redo functionality at various levels of task granularity, and presents the captured provenance in an accessible format to support a range of provenance queries for analysis. We also present several motivating use case scenarios and a user evaluation which suggests that our approach is both efficient and useful to scientists.