NeqSim — an Open-Source Process Simulation Software

NeqSim is a library for the calculation of fluid behavior, phase equilibrium, and process simulation. NeqSim can be used via various toolboxes or through a web interface. It can be integrated into computer programs via available interfaces in Java, Python, .NET, and MATLAB, or into process simulators via the CAPE-OPEN interface.

The basis for NeqSim is fundamental mathematical models related to unit operations, phase behavior, and physical properties of fluids. NeqSim is used for fluids such as oil and gas, carbon dioxide, refrigerants, hydrogen, ammonia, water, and chemicals.

Support related to the use and development of NeqSim is provided by the Department of Energy and Process Engineering at NTNU.

NeqSim — Key Capabilities

Advanced thermodynamics and property models
Integrated process simulation
PVT simulation
Flow assurance & production chemistry
Fluid flow & pipeline simulation
Production optimization (HTML / PDF)
Risk-based process safety analysis
Sustainability & emissions tracking
Field development and operations
Hydrogen production
Open, scriptable & extensible
Digital process twins & AI integration
Agentic Engineering (HTML / PDF)
Agentic Engineering for Operation (HTML / PDF)

NeqSim Project on GitHub

The NeqSim library is written in the Java programming language. The source code and libraries are hosted on GitHub.

NeqSim Java

Also see the experimental data and parameter fitting project.

NeqSim Toolboxes on GitHub

NeqSim toolboxes are available on GitHub for alternative programming languages.

NeqSim User Documentation

A comprehensive user manual is available for NeqSim, covering thermodynamic models, methods, and usage examples.

Getting Started

NeqSim can be integrated into computer programs via interfaces in Java, Python, .NET, and MATLAB.

NeqSim Discussions

Questions related to use and development can be asked on the NeqSim GitHub Discussions page.

Examples

Java

NeqSim API

NeqSim is well suited as a basis for developing APIs for thermodynamic and process calculations.

API development in Java API and Python API
Example of API usage from Python

NeqSimLive

NeqSimLive is a collection of container-based APIs used for simulation and performance monitoring of process plants. NeqSimLive APIs are typically consumed by company-specific tools for scheduling calculations, visualization, and data writing.

Support for developing digital twin components for flow assurance, process, and transport can be requested from the Energy and Process Technology group at NTNU.

NeqSim Web Applications

A web application has been developed to run calculations using NeqSim via a web interface. Calculations such as TPflash, dew points, phase envelopes, and hydrate equilibrium calculations can be performed in the web application. An alternative web interface is available via Google Colab (Python).

NeqSim AI

NeqSim Process Reinforcement Learning Agents is an open-source project that leverages multi-agent reinforcement learning (RL) to optimize oil and gas processes simulated using the NeqSim package. The framework allows intelligent agents to control different process components — compressors, valves, pumps, and heat exchangers — to minimize emissions, CO₂ footprint, power consumption, and heat input while maintaining product quality and operational stability.

NeqSim-Process-RL-Agents

Benchmark

See the NeqSim benchmark project.

A benchmark of computational speed is published on the benchmark page.

How to Cite NeqSim

If NeqSim contributes to a publication, report, or product, please cite it so the work can be traced and credited. The authoritative, machine-readable citation metadata is maintained in CITATION.cff in the main repository; GitHub renders this automatically as a “Cite this repository” button on the equinor/neqsim page, which also lets you export the citation in APA, BibTeX, or other formats.

APA-style citation (software):

Solbraa, E., & NeqSim Contributors. (2026). NeqSim: A library for thermodynamic and process simulation (Version 3.21.0) [Computer software]. Equinor. https://github.com/equinor/neqsim

BibTeX:

@software{neqsim2026,
  author       = {Solbraa, Even and {NeqSim Contributors}},
  title        = {NeqSim: A library for thermodynamic and process simulation},
  year         = {2026},
  version      = {3.21.0},
  publisher    = {Equinor},
  url          = {https://github.com/equinor/neqsim},
  license      = {Apache-2.0}
}

When citing the thermodynamic models underlying NeqSim rather than the software itself, cite the originating academic work:

@phdthesis{solbraa2002,
  author = {Solbraa, Even},
  title  = {Equilibrium and non-equilibrium thermodynamics of natural gas systems},
  school = {Norwegian University of Science and Technology},
  year   = {2002}
}

Always cite the specific NeqSim version used (see the version field above, or the release tag on GitHub Releases) so results remain reproducible as the library evolves. If you use one of the companion books or notebooks in this repository, cite the corresponding book/notebook in addition to the software itself; see each book’s own references/bibliography section for its recommended citation.