Factbox: Biggest civil penalties by U.S. energy regulator FERC

U.S. federal energy regulators have threatened to fine London-based Barclays about $470 million to settle claims that the bank and its traders manipulated California energy markets, in the largest proposed fine from the agency since 2005.

The Federal Energy Regulatory Commission's Office of Enforcement staff alleged Barclays engaged in a coordinated scheme to manipulate trading at four electricity trading points in the western United States from November 2006 to December 2008.

In an order issued Wednesday, FERC said Barclays has 30 days to show why the bank should not be penalized.

The following is a list of the biggest FERC civil penalties since the Energy Policy Act of 2005 significantly increased the fine the commission can impose to $1 million per day per violation from the prior cap of $10,000 a day.

Since 2007, FERC has issued $302.4 million in fines, excluding the proposed Barclays fine, according to its website (FERC Civil Penalty Action website: http://r.reuters.com/pec73t)

Disgorgement refers to the repayment of illegal profit.

Company; Civil Penalty; Disgorgement; Year

Barclays (proposed); $435 million; $34.9 million; 2012

Constellation; $135 million; $110 million; 2012

Atmos Energy; $6.4 million; $5.6 million; 2011

PacifiCorp; $3.9 million; ---; 2011

Brian Hunter; $30 million; ---; 2011

Noble Energy; $4 million; $160,000; 2010

Florida Blackout; $25 million; ---; 2009

Energy Transfer; $5 million; $25 million; 2009

Enserco; $1.4 million; ---; 2009

Amaranth; $7.5 million; ---; 2009

ProLiance Energy; $3 million; $196,000; 2009

Sequent Energy; $5 million; $53,700; 2009

Piedmont NatGas; $1.25 million; ---; 2009

Anadarko; $1.1 million; $232,400; 2009

ONEOK; $4.5 million; $1.9 million; 2009

Tenaska Marketing; $3 million; $2.0 million; 2009

Edison Mission; $7 million; $2 million; 2008

Constellation NewEnergy; $5 million; $1.9 million; 2008

BP Energy; $7 million; ---; 2007

Cleco; $2 million; ---; 2007

Columbia Gulf; $2 million; ---; 2007

Calpine; $4.5 million; ---; 2007

Bangor Gas; $1 million; ---; 2007

PacifiCorp; $10 million; ---; 2007

SCANA; $9 million; $1.8 million; 2007

Entergy Services; $2 million; ---; 2007

(Reporting by Eileen O'Grady in Houston and Scott DiSavino in New York; Editing by Lisa Shumaker)