When a firm sells (writes) an option, it receives the option premium upfront and is subject only to the potential obligation to deliver or buy the underlying asset if the option is exercised by the buyer. Because the buyer of the option has no future obligations to pay the seller, the seller has no counterparty credit exposure. Only the buyer of an option faces counterparty credit risk (the risk that the seller defaults on the payout). Therefore, the counterparty exposure for the derivative trading firm is EUR 0.