Large dealer banks have often financed significant fractions of their assets using short-term (overnight) repurchase agreements in which creditors hold bank securities as collateral against default losses. The table below shows the quarter-end financing of four A-rated broker-dealer banks. All values are in USD billion.

Financial instruments	Bank P	Bank Q	Bank R	Bank S
Owned	656	750	339	835
Pledged as collateral	258	472	139	209
Not pledged	398	278	200	626

In the event that repo creditors become equally nervous about each bank's solvency, which bank is most vulnerable to a liquidity crisis?