A flash stress in the market in September meant that cash available to short-term borrowers all but dried up as demand for funds to settle Treasury purchases and pay corporate taxes overwhelmed loans made available in the repurchase agreement (repo) market.

Interest rates in U.S. money markets shot up to as high as 10% for some overnight loans, more than four times the Fed’s rate.

Since September, the New York Federal Reserve has offered daily operations where it injects liquidity into the overnight market, in addition to frequent offerings of longer-term loans. It is the Fed’s first major market intervention since the financial crisis more than a decade ago.

Whether it will be enough to offset the traditional year-end strains will be tested next week, when companies will again face tax obligations while $78 billion in Treasury supply will also need to be settled. At the year-end there is also typically a reluctance by banks and fund managers to lend, which can leave borrowers struggling to raise cash.

Some fear that structural problems with the market leave it vulnerable to periods of stress.

The Bank for International Settlements said last week that growing reliance on the biggest U.S. banks to keep the repo market functioning may have been a big factor in September’s cash squeeze. [L8N28I0J2]

The big four banks, which BIS did not name in its report, have become net providers of funds to repo markets as they account for more than half of all Treasuries held by banks in the United States at the Federal Reserve.