Banks act to ease strains.
The European Central Bank, US Federal Reserve, the Bank of England and the central banks of Canada, Japan and Switzerland all took part in the operation.
The move sent stock markets up sharply yesterday.
The European Central Bank said it was making it cheaper for banks to get US dollar liquidity when they need it, starting next Monday.
They are also taking steps to ensure banks can get ready money in any currency if market conditions warrant.
The financial system had been showing signs of entering another credit crunch as Europe's debt crisis showed alarming signs of spreading, but stocks surged following the news.