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Electric Distribution 


  • 342,000 customers
  • 187 communities
  • Revenue by category 
    • 37% residential,
    • 51% commercial and industrial
    • 12% other
  • 17,500 miles of overhead and underground distribution lines
  • Service territory covers approximately
    73 percent of Montana's land area
  • 2012 peak demand 1,784 MW
  • Average daily load 1,237 MW

South Dakota  

  • 61,600 customers
  • 110 communities
  • Revenue by category
    • 39% residential
    • 57% commercial and industrial
    • 2% wholesale
    • 2% other 
  • 3,350 miles of overhead and underground distribution lines
  • 2012 peak demand 324 MW
  • Average daily load 172 MW

2012 Electric Sales Volumes (PDF) 
2011 Electric Sales Volumes (PDF) 
2010 Electric Sales Volumes (PDF) 
2009 Electric Sales Volumes (PDF) 
2008 Electric Sales Volumes (PDF) 
2007 Electric Sales Volumes (PDF) 
2006 Electric Sales Volumes (PDF)  

Electric Transmission 


  • 6,900 miles of transmission lines and associated terminal facilities
  • Voltage levels ranging from 50 kilovolts to 500 kilovolts
  • 286 circuit segments
  • Approximately 100,000 transmission poles
  • Extends throughout the western two-thirds of Montana from Colstrip in the east to Thompson Falls in the west
  • Jointly owns a 500 kilovolt transmission system that transfers electricity generated from the 2,180 megawatt Colstrip generation facility to markets within the state and west of Montana
  • Interconnections to five major nonaffiliated transmission systems located in the Western Electricity Coordinating Council (WECC) area
  • One interconnection to a system that connects with the Mid-Continent Area Power Pool (MAPP) region
  • Directly interconnected with Avista Corporation, Idaho Power Company, PacifiCorp, the Bonneville Power Administration and WAPA.

Transmission reservations for service over the Montana system occur on NorthWestern Energy's Open Access Same-Time Information System (OASIS) – Transmission service for both wholesale and deregulated retail access are provided under the FERC electric Open Access Transmission Tariff (OATT)located on the NorthWestern Energy OASIS site under the "Tariffs / FERC Filings" folder located on the left hand side of the OASIS page.

For more information about our Electric Transmission Services, you may contact us via email or call (406) 497-4500.

FERC Order 890 requires transmission providers to post on OASIS all of their business rules, practices, and standards that relate to transmission services provided under the pro forma OATT.  Below is a link to NorthWestern Energy's OASIS (

South Dakota

  • Voltage levels ranging from 34.5 kilovolts to 345 kilovolts
  • Extends throughout the middle of eastern South Dakota along the James River
  • Interconnections to major transmission system in Mid-Continent Area Power Pool (MAPP) region and Midwest Independent System Operator (MISO). We have interconnections with Western Area Power Administration, Montana-Dakota Utilities Co., Otter Tail Power Company and Xcel Energy.
  • Emergency interconnections with East River Electric Cooperative, Inc. and West Central Electric Cooperative

Transmission reservation for service over the South Dakota system occurs on WAPA (IS): Open Access Same-Time Information System (OASIS)

Transmission service for both wholesale and deregulated retail access are provided under the NorthWestern-South Dakota FERC:  Open Access Transmission Tariff (OATT)

For more information about our Electric Transmission Services, you may contact us via email or call (605) 353-7465.

FERC Order 890 requires transmission providers to post on Web site all of their business rules, practices and standards that relate to transmission services provided under the pro forma OATT. Below are the links to NorthWestern Energy's documents.

The following South Dakota local area planning documents are posted pursuant to the South Dakota Attachment K.

The following document is posted for information purposes at this time and is South Dakota’s FERC Order 1000 response for public policy posting requirements.

NorthWestern has requested an effective date of October 1, 2013 for implementation of FERC Order 1000. Until then the following information is informational.

Electric Supply


  • Owned generation resources supply approximately 23% of our retail load requirements.
  • Our joint ownership interest in Colstrip Unit 4, a 740 MW demonstrated-capacity coal-fired power plant located in southeastern Montana, provides base-load supply.
  • We purchased and placed into service in the fourth quarter of 2012 the 40 MW Spion Kop wind project.
  • Our remaining customer load requirements are met with market purchases from third parties and include resources from wind generation, gas-fired generation and seasonal base-load hydro supply.
  • Our Dave Gates Generating Station at Mill Creek, a 150 MW natural gas fired facility, primarily provides regulation service. 

South Dakota
  • Our South Dakota electric supply load requirements are primarily provided by three jointly owned coal-fired generating plants:     
    • Big Stone Plant  (Big Stone City, S.D.) 
    • Coyote Electric Generating Station (Beulah, N.D.)
    • Neal Electric Generating Unit No. 4 (Sioux City, Iowa)
  • We also own several peaking/standby generating units located throughout our service territory.
  • We use market purchases and peaking generation to provide peak supply in excess of our base-load capacity.
  • In 2012, 93% of the electricity utilized in South Dakota came from coal, 6% from a wind purchased power contract and 1% from natural gas and fuel oil.

Natural Gas Distribution 


  • 183,300 customers
  • 105 communities
  • 5,000 miles of distribution gas pipelines



South Dakota/Nebraska 

  • 86,300 customers
  • 60 communities in South Dakota
  • 4 communities in Nebraska
  • 2,350 miles of distribution gas pipelines

2012 Natural Gas Sales Volumes (PDF)
2011 Natural Gas Sales Volumes (PDF)
2010 Natural Gas Sales Volumes (PDF)
2009 Natural Gas Sales Volumes (PDF)
2008 Natural Gas Sales Volumes(PDF)
2007 Natural Gas Sales Volumes(PDF)
2006 Natural Gas Sales Volumes(PDF)

Natural Gas Transmission 


  • We transmit natural gas in Montana from production receipt points and storage facilities to distribution points and other nonaffiliated transmission systems
  • 2,000 miles of transmission pipelines
    • 2" to 24" diameter pipelines
    • 130 city gate stations
  • Connections with five major nonaffiliated transmission systems
    • Williston Basin Interstate Pipeline
    • NOVA Gas Transmission Ltd.
    • Colorado Interstate Gas
    • Spur Energy 
    • Havre Pipeline
  • 7 compressor stations capable of moving more than 335,000 dekatherms per day
  • Own and operate a pipeline border crossing from Canada through our wholly owned subsidiary, Canadian-Montana Pipe Line Corporation
  • 17.75 Bcf of gas storage capacity 
    • Own and operate three working natural gas storage fields
    • Maximum aggregate daily deliverability of approximately 195,000 dekatherms per day

South Dakota

  • 55 miles of transmission pipelines

Natural Gas Supply

  • We have municipal franchises to transport and distribute natural gas in the Montana communities we serve. The terms of the franchises vary by community.
  • Montana natural gas supply requirements are primarily fulfilled through third-party fixed-term purchase contracts and short-term market purchases.
  • We utilize a portfolio approach to fulfill our natural gas supply requirements, and we have direct access to suppliers in the major natural gas producing regions in the U.S., namely, the Rockies (Colorado), Montana and Alberta, Canada.
  • Since 2010, we have acquired gas production and gathering system assets that are estimated to provide approximately 1.8 Bcf each year, or about 10% of our current annual natural gas load in Montana.  

South Dakota/Nebraska

  • We have municipal franchises to purchase, transport and distribute natural gas in the South Dakota and Nebraska communities we serve. The terms of the franchises vary by community.
  • South Dakota transportation and storage of supply are managed by a third party.
  • Nebraska asset management services for pipeline capacity, supply, and asset optimization are fulfilled through a third party.
  • We contract for firm natural gas storage services to meet heating season and peak day requirements in South Dakota and Nebraska.
  • We operate a propane-air gas peaking unit to meet peak day demands.
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