Quoted from: https://www.diw.de/de/diw_01.c.599753.de/modelle.html#ab_599760 

OILMOD is a numerical partial equilibrium model of the international crude oil market. The producer-focussed model allows to investigate the consequences of climate and market policies as well as different sector developments such as technical innovation. Crude oil exporting countries are modelled as profit-maximising suppliers in oligopolistic quantity competition. Different versions of the model feature refinery, node-to-node transportation, endogenous investments, and varying competition setups.
As the crude oil market is dominated by a small number of large producers as well as the presence of the Organisation of the Petroleum Exporting Countries (OPEC), the market can hardly be defined as competitive. Therefore, OILMOD allows for a flexible approach of modelling different (asymmetric) competition set-ups by using conjectural variation and an explicit formulation of multi-level frameworks, i.e. sequential decision-making in production quantities.
The model is formulated and solved as a mixed coplanarity problem (MCP) in the General Algebraic Modeling System (GAMS) using the solver PATH, using MS Excel for data processing and output reports. The multi-level formulation of OILMOD is formulated as a mixed-integer nonlinear problem (MINLP) and solved using BONMIN.