Significant portions of assets for A-rated broker-dealer banks have frequently been financed by large dealer banks through short-term (overnight) repurchase agreements (repos). In these agreements, creditors hold the bank securities as collateral to safeguard against potential defaults. The table below details the quarter-end financing for four such broker-dealer banks, with figures presented in USD billions:

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

Given these conditions, if repo creditors universally have equivalent concerns about the solvency of each bank, determine which bank would be at the greatest risk of experiencing a liquidity crisis.