High-quality assets play an important role as collateral for a wide range of transactions and activities in wholesale financial markets. Regulatory changes introduced since the global financial crisis are increasing the demand for high-quality assets, thereby raising concerns about possible shortages. Drawing on data from a survey of securities dealers' collateral activity in the Australian market in 2014 and 2016, this paper attempts to quantify the "effective" supply of collateral assets in Australia by applying a measure of supply that adjusts outstanding issuance for two important features of the collateral market. One feature is that a large proportion of Australian highquality assets are held by long-term investors that do not make these assets available for sale, loan or use in repurchase agreements. A second feature is the ability to reuse collateral assets, thereby allowing a single piece of collateral to meet multiple demands. Using this measure, the current effective supply in 2016 is estimated to be around A$123 billion, comprising around A$99 billion of active supply that is reused on average 1.25 times. This amount has remained largely unchanged since the 2014 survey, due to broadly offsetting changes in total source collateral and the rate of collateral reuse.