Gas and oil separation plant (GOSP) is a very important first step in any oil production facility. Major oil fields normally consist of tens of such GOSPs. These GOSPs are big electricity consumers due to the work of oil and water pumps; water injection pumps and associated gas compressors. Therefore they are also big GHG emission producers. The allocation of the oil and associated gas output of hundreds of oil wells to these GOSPs is not a very straight forward task since these GOSPs have oil and gas handling systems and pumps& compressors with different capacities and energy consumption efficiencies.

In this paper an optimal allocation model of the oil and its associated gas produced from hundreds of oil wells to these GOSPs while reducing energy consumption and GHG emission is introduced. A graphical method is applied first using source-sink mapping techniques to get preliminary and initial solutions to the optimal allocation problem. The problem is formulated as mixed integer optimization problem due to the discrete decisions related to oil pumps and gas compressors. Constraints logic propagation technique is used first to check feasibility of the problem exhibited in the production of the desired amount of crude oil per day before optimizing energy consumption and GHG emission. The model formulated for the constraints logic propagation environment can be used as it is, upon proving feasibility, to find the details of the allocation problem solution that renders minimum energy consumption and GHG emission using mathematical programming. An industrial case study of typical oil filed with about fifty gas oil separation plants (GOSPs) is also introduced.