BEIJING, May 20 -- China's central bank on Friday pumped 20 billion yuan (3.06 billion U.S. dollars) into the market to preserve liquidity.

The People's Bank of China (PBOC) put 50 billion yuan into seven-day reverse repos priced to yield 2.25 percent.

Reverse repos worth 30 billion yuan mature on Friday, so the central bank has effectively injected 20 billion yuan into the market.

On Friday's interbank market, the benchmark overnight Shanghai Interbank Offered Rate (Shibor) was down by 0.2 basis point to 2.008 percent.

Seven-day Shibor stayed unchanged at 2.331 percent. Three-month Shibor rose 0.15 basis point to 2.9288 percent.

The PBOC has pumped a net total of 50 billion yuan into the market this week, ending the consecutive currency withdrawal of the previous three weeks.