The level of commercial bank reserves is determined by the size of the Fed’s balance sheet, and the proportion of reserves that end up in the Fed accounts of banks. When the Fed purchases securities or makes loans, it creates reserves out of thin air to fund them. A $100 purchase of Treasury securities results in the creation of $100 in reserves. A $100 FX Swap loan also creates $100 in reserves. Reserves can only be created or destroyed by the Fed, but banks are not the only entities eligible to hold reserves.

Reserves can never leave the Fed’s balance sheet, but they can be shifted around the Fed’s balance sheet. Think of it as Bitcoin ledger, where Bitcoins are paid to other wallets but always remain on the ledger. Only entities with an account at the Fed can hold reserves, so the created reserves are shuffled amongst the different Fed account holders as payments are made. For example, when commercial bank A makes a payment to commercial bank B, then reserves are wired from bank A’s Fed account to bank B’s Fed account. The total level of reserves stays the same. Most reserves are held by depository institutions such as commercial banks or credit unions, but there are other notable entities that have Fed accounts. These other entities, such as the Treasury, can at times have large holdings of reserves. The level of reserves held by the banking sector decreases when reserves move into these other Fed accounts.

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