This paper introduces a methodology to estimate the re-use of collateral based on actual transaction data. With a comprehensive data set from the Swiss franc repo market we are able to provide the first systematic study on the re-use of collateral. We find that re-using collateral was most popular prior to the financial crisis when roughly 10% of the outstanding interbank volume was secured with re-used collateral. Furthermore, we show that the re-use of collateral increases with the scarcity of collateral. By giving an estimate of the collateral re-use and explaining its drivers, the paper contributes to the on-going debate on collateral availability.