NeqSim is a library for estimation of behaviour and properties of fluids. NeqSim is available for free use and distributed as open source under the Apache-2.0 licence.


22/09/2022: Version 2.4.0 released

Contact project via email

NeqSim - an open source process simulation software

NeqSim is a library for calculation of fluid behavior, phase equilibrium and process simulation. NeqSim can be used as a stand-alone tool via Excel or a web interface. It is integrated in computer programs via available interfaces in Java, Python, .NET, Matlab or in process simulators via the Cape Open interface. The basis for NeqSim is fundamental mathematical models related to unit operations, phase behaviour and physical properties of fluids. NeqSim is used for fluids such as oil and gas, carbon dioxide, refrigerants, hydrogen, ammonia, water and chemicals.

The original NeqSim web page is hosted at NTNU

NeqSim project in GitHub

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

NeqSim toolboxes in GitHub

NeqSim toolboxes are avalable via GitHub for alternative programming languages.

Getting started

NeqSim is integrated in computer programs via interfaces in java, python, .NET and Matlab.

NeqSim discussion

Questions related to use and development are asked on the NeqSim github discussions page.






Excel/Cape Open

NeqSim API

NeqSim is well suited for beeing the basis for developing API’s for thermodynamic and process calculations.


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 writing of data. Support on developing digital twin components for flow assurance, process and transport can be reqested from the Energy and Process Technology group at NTNU.

NeqSim web application

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


A benchmark of computational speed of the frameworks is published in the benchmark page