The market for corporate borrowing via commercial paper contracted to the lowest level in more than two months as U.S. financial institutions turned more to central banks for funding.

The seasonally adjusted amount of U.S. commercial paper dropped $18.1 billion to $990.1 billion outstanding in the week ended yesterday, the fourth straight decrease, the Federal Reserve said today on its website. It's the longest stretch of declines since the period ended March 7 and the least since the market touched $982.5 billion in the period ended July 18, according to Fed data compiled by Bloomberg.

Financial borrowers have relied increasingly on central banks for funding as demand has declined for short-term obligations on concern that Europe's sovereign-debt turmoil may contaminate balance sheets globally. The Fed said on Sept. 13 it will expand its holdings of long-term securities with purchases of $40 billion of mortgage debt a month in an additional round of so-called quantitative easing.