Presentation given on October 27, 2016 at Data Reproducibility: Integrity and Transparency program as part of Open Access Week 2016. / We describe a study into the extent to which Computer Systems researchers share their code and data. Starting with 601 papers from ACM conferences and journals, we examine the papers whose results were backed by code to see for what fraction of these we would be able to obtain and build the code. Based on the results of this study, we propose a novel sharing specification scheme that requires researchers to specify the level of sharing that reviewers and readers can assume from a paper.