Is This Normal? The Cost of Assuming that Derivatives Have Normal Returns

Derivatives exchanges often determine collateral requirements, which are fundamental to market safety, with dated risk models assuming normal returns. However, derivatives returns are heavy-tailed, which leads to the systematic under-collection of collateral (margin). This paper uses extreme value theory (EVT) to evaluate the cost of this margin inadequacy to market participants in the event of default. I find that the Canadian futures market was under-margined by about $1.6 billion during the Great Financial Crisis, and that the default of the highest-impact participant generates a cost of up to $302 million to be absorbed by surviving participants. I show that this cost can consume the market’s entire default fund and result in costly risk mutualization. I advocate for the adoption of EVT as a benchmarking tool and argue that the regulation of exchanges should be revised for financial products with heavy tails.