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Economic Brief

February 2019, EB19-02

Large Excess Reserves and the Relationship
between Money and Prices
By Huberto M. Ennis and Tim Sablik

As a consequence of the Federal Reserve’s response to the financial crisis of
2007–08 and the Great Recession, the supply of reserves in the U.S. banking
system increased dramatically. Historically, over long horizons, money and
prices have been closely tied together, but over the past decade, prices have
risen only modestly while base money (reserves plus currency) has grown substantially. A macroeconomic model helps explain this behavior and suggests
some potential limits to the Fed’s ability to increase the size of its balance sheet
indefinitely while remaining consistent with its inflation-targeting policy.
Macroeconomic models have long predicted a
tight long-run relationship between the supply
of money in the economy and the overall price
level. Money in this context refers to the quantity
of currency plus bank reserves, or what is sometimes called the monetary base. As the monetary
base increases, prices also should increase on a
one-to-one basis.
This theory also has been confirmed empirically.
According to Robert Lucas of the University of
Chicago, who received the Nobel Prize in Economics in 1995 in part for his work in this area,
“The prediction that prices respond proportionally to changes in money in the long run … has
received ample — I would say, decisive — confirmation in data from many times and places.”1
But recent events have called the relationship Lucas spoke of into question. Over the past decade,
the monetary base in the United States grew at
an average annual rate of 16 percent as the Federal Reserve dramatically increased the amount

EB19-02 - Federal Reserve Bank of Richmond

of reserves in the banking system in response
to the financial crisis of 2007–08 and the Great
Recession. At the same time, prices grew at only
1.8 percent per year on average. This Economic
Brief provides one explanation for this behavior
and examines whether there might be limits to
the decoupling of money from prices.
A Period of “Unconventional” Policy
In response to the financial crisis of 2007–08,
the Fed employed a number of extraordinary
measures to stabilize the financial system and
help the economy weather the Great Recession.
Between the summer of 2007 and the end of
2008, the Fed created several lending facilities
to provide liquidity to the financial system while
the Federal Open Market Committee (FOMC)
brought its target for the federal funds rate down
from 5.25 percent to effectively zero. With no
more room to cut rates, the Fed turned to more
unconventional policies, such as large-scale asset
purchases known as “quantitative easing” (QE).
The Fed used QE and related programs (such as

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Operation Twist) in an effort to lower long-term interest rates to stimulate the economy and spur recovery
from the Great Recession.2 These actions grew the
Fed’s balance sheet to roughly $4.5 trillion.
In order to pay for the QE purchases, the Fed issued
reserves.3 Banks have always been required by law to
hold some reserves, but historically they have held
very little in the way of “excess” reserves because the
opportunity cost of doing so was high. Before 2008,
reserves paid no interest, so choosing to hold excess
reserves meant banks would need to forgo whatever
interest they could earn in the market. Banks that
found themselves short of their reserve requirement
at the end of the day could borrow them overnight
from banks that ended the day with a surplus, further reducing any incentives to hold excess reserves.
This low-reserve environment was intertwined with
how the Fed traditionally set monetary policy. The
Fed’s target policy rate, the fed funds rate, is the rate

that banks charge one another to borrow reserves
overnight. By changing the supply of reserves in the
market, the Fed could target the fed funds rate it
desired, executing monetary policy in line with the
decisions of the FOMC.
In October 2008, the Fed gained the authority to pay
interest on reserves, allowing it to set a floor for market rates while increasing the supply of reserves in the
banking system. This tool soon became less important
as the Fed’s target rate fell closer to its effective lower
bound in December 2008. But, in general, by paying
interest on reserves, the Fed could give banks greater
incentives to hold excess reserves than in the past.
From late 2008 through 2014, the amount of reserves
in the banking system grew significantly as a result
of the lending facilities and the QE programs, with
reserves becoming a much larger proportion of total
assets on banks’ balance sheets. (See Figure 1.) At

Figure 1: Composition
of U.S.
Commercial Bank
Assets
before and
after 2008
U.S.
Commercial
Bank
Assets
before
and a�er

2008

100
100
9090
8080

Percent of Assets

Percent of assets

7070
6060
5050
4040
3030
2020
1010
0

2000

2002

2004
Cash Assets

2006

2008

2010

Loans and Leases

2012

2014

2016

2018

Securities

CashReserve
Assets
and Leases
Securi�es
Source: Board of Governors of the Federal
System, Loans
H.8 Release
Notes: Cash assets are largely composed of bank reserves (balances due from Federal Reserve Banks) and vault cash. Securities include
Treasury and agency debt, mortgage-backed securities, and other securities. Loans and leases include commercial and industrial loans,
real estate loans, consumer loans, and other various smaller categories of loans. The remaining assets are accounted for by various small
categories, such as federal funds sold and reverse repurchase agreements.

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various times during the unconventional monetary
policy period, many policymakers expressed concerns that the massive increase in reserves from QE
could eventually trigger inflation. For example, in a
2012 speech, then Philadelphia Fed President Charles
Plosser warned that “once the recovery strengthens
— and it surely will — long rates will begin to rise and
banks will begin lending out their excess reserves. …
In such an environment, policymakers might need
to tighten policy quickly to contain inflationary
pressure.”4 But as the recovery proceeded, inflation
remained low despite the unprecedented level of
excess reserves in the system. Why?
Modeling an Economy with Large Excess Reserves
To improve our understanding of this issue, it is
useful to study a model of the macroeconomy that
explicitly includes a banking system with a nontrivial
balance sheet. In a recent paper, one of the authors
of this Economic Brief (Ennis) studies such a model.5
In the model, bankers can make loans and also can
borrow from other banks in the interbank market.
There is a central bank that controls the total supply
of monetary assets (reserves plus currency) in the
economy but not the split (that is, banks determine
whether to hold reserves or transform them into
currency). In the model, as in reality, only banks can
hold reserves.
When reserves are “scarce” or when banks have no
reason to hold excess reserves (for example, because
reserves pay no interest), the model predicts that
there will be little to no demand for excess reserves.
Under these conditions, prices move together with
the quantity of monetary assets. This aligns well
with the observed real-world, long-run relationship
between prices and monetary assets that Lucas
referred to in his 1995 lecture.
On the other hand, if the central bank pays interest
on reserves at market rates, banks are willing to hold
excess reserves, and prices no longer need to move
in step with the quantity of money. In this situation,
the quantity of reserves in the banking system could
increase considerably without any significant effect
on the price level. This configuration closely matches

the monetary behavior of the U.S. economy over the
past decade.
Limits to the Decoupling of Money and Prices
As experience demonstrates — and Ennis’s model
explains — paying a market rate on reserves allows
a central bank to increase the supply of monetary
assets without generating a corresponding response in the price level. But does the central bank
face limits in its ability to continue increasing the
supply of reserves while maintaining a stable price
level? In September 2012, the Fed announced its
third QE program. This program differed from the
first two in that the Fed agreed to purchase a fixed
amount of assets ($85 billion) per month “indefinitely.” Simultaneously, the Fed pledged to maintain its inflation target of 2 percent. The fact that
the program had no fixed duration implied that the
total increase in the size of the balance sheet and,
in particular, excess reserves in the banking system
were left unspecified.
Relatedly, the recently released FOMC transcripts for
2013 reveal that some participants at the time worried about the possibility of facing limits in the Fed’s
ability to continue QE purchases for an extended
period of time. In the April/May 2013 meeting, then
Dallas Fed President Richard Fisher asked “what the
practical limits are on the size of our balance sheet.”6
Fed staffers recognized the uncertainty and complexity of the question while also acknowledging
that a limit must exist as eventually “there won’t be
anything left for us to buy.” Ultimately, the Fed ended
asset purchases in 2014 before these issues became
more pressing, but the question of potential limits
to QE remains pertinent for future policymakers.
Beyond the extreme case of running out of assets
to buy, there may be other, more subtle limits to the
Fed’s ability to increase the size of its balance sheet
without triggering a corresponding increase in the
price level. Ennis’s model suggests one such limit. In
particular, the model indicates that a growing supply
of reserves eventually could become incompatible
with stable prices even if the central bank has the
authority to pay interest on reserves. Because only

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banks can hold reserves, the amount of reserves they
can hold is tied to the size of their balance sheets. If
banks face capital requirements (due to regulation or
other market-induced reasons), then the total value
of reserves that banks can hold is linked to the total
amount of bank capital available in the economy.
Eventually, as bank capital becomes scarce, the cost
of holding additional reserves becomes higher than
the interest paid on reserves and banks again become sensitive to the quantity of reserves outstanding. At this point, the model predicts that prices
would once again move together with the quantity
of monetary assets.
Looking Forward
The potential limits identified by the model never
materialized for the Fed in the aftermath of the Great
Recession, but knowing about them may prove useful for policymakers in the future.7 After the third QE
ended, the Fed maintained the size of its balance
sheet by reinvesting any securities that matured.
Starting in October 2017, the Fed began a process of
normalization for its balance sheet by reducing the
value of securities it reinvests by a fixed amount each
month. That said, many economists and Fed officials
anticipate that the Fed’s balance sheet will remain
larger than prior to the crisis of 2007–08 at least for
some time to come.
At the same time that it has been normalizing its balance sheet, the Fed also has been raising its target for
interest rates. The ability to pay interest on reserves
has been crucial to allowing the Fed to raise its target
rate while there are still significant excess reserves
in the banking system. Despite these rate increases,
due to various secular reasons, interest rates are
expected to remain historically low for a long time.
This could mean that the unconventional tools that
the Fed employed during the last crisis may become
more common in future downturns if the effective
lower bound on interest rates again becomes binding for the conduct of monetary policy. Improving
our understanding of the workings of such tools,
and their limitations, is therefore an important objective of economic research, and the model and ideas
discussed here contribute to that collective effort.

Huberto M. Ennis is the group vice president for
macro and financial economics, and Tim Sablik is
an economics writer in the Research Department
at the Federal Reserve Bank of Richmond.
Endnotes
1

R
 obert E. Lucas Jr., “Nobel Lecture: Monetary Neutrality,”
Journal of Political Economy, August 1996, vol. 104, no. 4,
pp. 661–682.

2

T he Fed’s Maturity Extension Program and Reinvestment
Policy that began in September 2011 and ran through the
end of 2012 was called “Operation Twist,” in reference to a
similar program the Fed employed in the 1960s. In the more
recent case, the Fed sold a total of $667 billion in short-term
Treasuries and used the proceeds to buy longer-term Treasuries. This was a way for the Fed to put downward pressure
on longer-term interest rates and provide additional easing
during the recovery from the Great Recession. See Tim Sablik,
“Jargon Alert: Operation Twist,” Federal Reserve Bank of Richmond Region Focus, Fourth Quarter 2012, p. 10.

3

S ee Todd Keister and James J. McAndrews, “Why Are Banks
Holding So Many Excess Reserves?” Federal Reserve Bank of
New York Current Issues in Economics and Finance, December
2009, vol. 15, no. 8.

4

C
 harles I. Plosser, “Good Intentions in the Short Term with
Risky Consequences for the Long Term,” Speech at the Cato
Institute 30th Annual Monetary Conference, Washington,
D.C., November 15, 2012. See also Huberto M. Ennis and
Alexander L. Wolman, “Excess Reserves and the New Challenges for Monetary Policy,” Federal Reserve Bank of Richmond Economic Brief No. 10-03, March 2010.

5

H
 uberto M. Ennis, “A Simple General Equilibrium Model of
Large Excess Reserves,” Journal of Monetary Economics, October
2018, vol. 98, pp. 50–65. Other papers that also have studied
this question include Mark Gertler and Peter Karadi, “A Model
of Unconventional Monetary Policy,” Journal of Monetary
Economics, January 2011, vol. 58, no. 1, pp. 17–34; Vasco Cúrdia
and Michael Woodford, “The Central-Bank Balance Sheet as an
Instrument of Monetary Policy,” Journal of Monetary Economics,
January 2011, vol. 58, no. 1, pp. 54–79; and Stephen D. Williamson, “Interest on Reserves, Interbank Lending, and Monetary
Policy,” Journal of Monetary Economics, forthcoming.

6

“ Meeting of the Federal Open Market Committee,” April 30May 1, 2013, pp. 114–115.

7

E nnis and Wolman study in detail the distribution of reserves
across banks in the United States and document that most of
the banks holding large excess reserves during the QE period
were not facing tight capital constraints. See Ennis and Wolman, “Large Excess Reserves in the United States: A View from
the Cross-Section of Banks,” International Journal of Central
Banking, January 2015, vol. 11, no. 1, pp. 251–289.

This article may be photocopied or reprinted in its
entirety. Please credit the authors, source, and the

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Federal Reserve Bank of Richmond and include the
italicized statement below.
Views expressed in this article are those of the authors
and not necessarily those of the Federal Reserve Bank
of Richmond or the Federal Reserve System.

FEDERAL RESERVE BANK
OF RICHMOND
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