The National Energy Modelling System (NEMS) is a large, regional, energy-economy-environmental model of U.S. energy markets . It is developed by the Energy Information Administration (EIA) which is part of the United States government, and the first release was in 1993. A new version of the model is produced every year and it has approximately 20 users. NEMS is free but it requires Fortran, EViews, IHS Global Insight model, OML (a linear programming package) to run which must be purchased. The training required is very diverse depending on the user’s requirements: the model has 12 modules which can be used together or separately.
Overall, NEMS represents the behaviour of energy markets and their interactions with the U.S. economy on an annual basis up to the year 2030. The model achieves a supply/demand balance in the end-use demand regions, defined as the nine Census divisions, by solving for the prices of each energy product that will balance the quantities producers are willing to supply with the quantities consumers wish to consume. The system reflects market economics, industry structure, and existing energy policies and regulations that influence market behaviour. NEMS consists of four supply modules (oil and gas, natural gas transmission and distribution, coal, and renewable fuels); two conversion modules (electricity and petroleum refineries); four end-use demand modules (residential, commercial, transportation, and industrial); one module to simulate energy/economy interactions (macroeconomic activity); one module to simulate world oil markets (international energy activity); and one module that provides the mechanism to achieve a general market equilibrium among all the other modules (integrating module). The only notable technologies that are not considered in NEMS are wave, tidal, CAES and hydrogen (although hydrogen transportation technologies can be accounted for). Each market segment is modelled so as to simulate the behaviour of that market. The modularity of the NEMS design provides the flexibility for each component of the U.S. energy system to use the methodology and coverage that is most appropriate and also, to execute the modules individually or in collections of modules, which facilitates the development and analysis of the separate component modules. The interactions among these modules are controlled by an integrating module. The results from NEMS project the energy, economic, environmental, and security impacts on the United States, of alternative energy policies and of different assumptions about energy markets.
NEMS is used every year to create the US Annual Energy Outlook . It has also been used in previous studies to evaluate the future options for coal-fired power-plants in the US , to analyse the impact of carbon reduction policies on the electricity sector , and to present the cost, energy, carbon savings by implementing more energy-efficient technologies in the US building sector  and to assess the impact of renewables on the US energy markets . Also, the NEMS model has simulated a renewable-energy penetration of 25% for the electricity sector and 12% of the transport sector . Finally, a full list of reports using NEMS is available at  and the accuracy of previous projections from the NEMS model have been discussed in .
- The National Energy Modeling System: An Overview 2003, Energy Information Administration, 26th April 2009, http://www.eia.doe.gov/oiaf/aeo/overview/index.html
- Archive Listing of Annual Energy Outlook Forecasts & Related Products Energy Information Administration, 26th April 2009, http://www.eia.doe.gov/oiaf/archive.html
- Geisbrecht, R. & Dipietro, P., Evaluating options for US coal fired power plants in the face of uncertainties and greenhouse gas caps: The economics of refurbishing, retrofitting, and repowering. Energy Procedia, 1(1), pp. 4347-4354, 2009.
- Hadley, S. W. & Short, W., Electricity sector analysis in the clean energy futures study. Energy Policy, 29(14), pp. 1285-1298, 2001.
- Koomey, J. G., Webber, C. A., Atkinson, C. S. & Nicholls, A., Addressing energy-related challenges for the US buildings sector: results from the clean energy futures study. Energy Policy, 29(14), pp. 1209-1221, 2001.
- Kydes, A. S., Impacts of a renewable portfolio generation standard on US energy markets. Energy Policy,35(2), pp. 809-814, 2007.
- Energy and Economic Impacts of Implementing Both a 25-Percent Renewable Portfolio Standard and a 25-Percent Renewable Fuel Standard by 2025, Energy Information Administration, 2007,http://www.eia.doe.gov/oiaf/servicerpt/eeim/pdf/sroiaf(2007)05.pdf.
- Responses to Congressional and Other Requests, Energy Information Agency, 26th April 2009,http://www.eia.doe.gov/oiaf/service_rpts.htm
- O’Neill, B. C. & Desai, M., Accuracy of past projections of US energy consumption. Energy Policy, 33(8), pp. 979-993, 2005.