According to the Federal Reserve’s Website as of December 31, 2009 any “depository institution” (bank) in the U.S. with more than $55.2 million in deposits must have at least 10% of their deposits (what banks call “liabilities”) on reserve. Most banks in the U.S. have far more than $55.2 million in total deposits, so they are subject to this 10% requirement. Smaller banks, however, have lower reserve requirements. Banks with less than $10.2 million in deposits are not required to hold any reserves and banks that have between $10.2-$55.2 million in deposits are subject to only a 3% reserve requirement.
As stated in the “Reserve Requirements” section of the Federal Reserve site, the Board of Governors has “ sole authority over changes in reserve requirements.”
To learn more about how “fractional reserve” lending works, you can check out: Modern Money Mechanics by The Federal Reserve Bank of Chicago; Money as Debt by Paul Grignon; or Dollar Deception: How Banks Secretly Create Money by Ellen Brown.