Liquid Fuels Market Module - NEMS Documentation
August 2025
Introduction
The Natural Gas Market Module (NGMM) is the component of the National Energy Modeling System (NEMS) that represents the North American natural gas transmission and distribution system. We developed the NEMS as the third in a series of computer-based energy-economy modeling systems. EIA and its predecessor, the Federal Energy Administration, have used NEMS to analyze and project U.S. domestic markets to provide 25–30 year projections and to analyze a broad range of energy issues at both national and regional levels. Although the NEMS was first used in 1992, the model is updated each year; updates in individual modules range from simple historical data updates to completely replacing submodules. The NGMM was an entirely new model we incorporated into the NEMS for the Annual Energy Outlook 2018, replacing the Natural Gas Transmission and Distribution Module (NGTDM).
Documentation purpose and scope
This report provides a reference document for model analysts, users, and the public that defines the objectives of the Natural Gas Market Module (NGMM) in the NEMS. This report also fulfills EIA’s legal obligation to provide adequate documentation in support of our models under Public Law 93-275, Federal Energy Administration Act of 1974, Section 57(B)(1) (as amended by Public Law 94-385, Energy Conservation and Production Act).
In this report, we:
- Describe NGMM’s basic design
- Provide details on the methodology employed
- Detail the model inputs, outputs, and key assumptions
Because we first incorporated the NGMM into the NEMS for the Annual Energy Outlook 2018, the documentation also describes our decision to build a new model in the NEMS to represent natural gas markets and the differences between the NGMM and its predecessor.
This report is also a reference document for how the NGMM uses Advanced Integrated Multidimensional Modeling Software (AIMMS)1 and AIMMS best practices for the NEMS. The NGMM is the second module (after the Coal Market Module) we developed and implemented in the NEMS using the AIMMS modeling language and user interface, and we expect to develop all future optimization models in AIMMS.2 Therefore, this documentation report uses AIMMS terminology to describe in detail the most efficient, flexible, and transparent techniques and methods employed in the NGMM. This aspect of the report is particularly important to ensure the reproducibility of results, given thecomplexity of NEMS runs and the exchange of data between the NEMS Fortran code, the NGMM AIMMS code, and various external files.
Notes and sources
1 AIMMS Development Environment is software that integrates the AIMMS mathematical modeling language, a graphical user interface, and numerical solvers. It is used to design and build optimization models and includes diagnostic tools as well as the ability to construct graphical reports of model results. Available AIMMS documentation includes AIMMS—The Language Reference and AIMMS—The User’s Guide.
2 AIMMS, The U.S. Department of Energy expands its use of AIMMS for its NEMS Electricity Market Module