Theory predicts that slack resources provide the means for achieving flexibility in developing strategy options. The outcome of generating and investing slack resources to achieve flexibility should be improved company performance. There is also a prediction that low performing companies are likely to have lower levels of slack than high performing companies, and therefore are likely to have less potential for achieving flexibility to impact on performance. However, as the literature features several inadequacies a comparative study of high and low performing British companies was carried out to address these inadequacies. While multiple measures of slack were found to be predictors of company performance in high performing companies, they seemingly have negligible impact on performance in low performing companies. Also, only certain types of slack resources are seemingly more prominent in high performers than in low performers. The results provide a development and refinement of the previous limited knowledge about slack resources.