SAN FRANCISCO (MarketWatch) -- The Federal Reserve injected roughly $6 billion into the banking system on Thursday.

The Fed carried out three repurchase agreements totaling $47.25 billion, according to the Web site of the Federal Reserve Bank of New York.

The first was a 14-day, $8 billion repo on Thursday morning. The second was a six-day, $20 billion repo roughly an hour later. The third was a one-day, $19.25 billion repo. The Fed accepted more than $20 billion of mortgage-backed securities as collateral in the moves, the Web site said.

Other agreements were expiring, so the Fed ended up adding roughly $6 billion in extra liquidity into the system, said Lou Crandall, chief economist at Wrightson ICAP.