Modern reservoir simulation models of oil and gas fields become more detailed, calculated cells become smaller, and the number of these cells avalanche grows. For large and giant oil fields the number of cells in such models can reach up to 109. The authors have developed and tested computing technology that removes the constraints on the size and detail of reservoir simulation models. This technology is based on the decomposition of large models for sector models and on separate calculations. Algorithm of iterative integration of sector models-Iterative Fitting Boundary Conditions (IFBC) restores the integrity of the full model. This algorithm is more general than option Flux Boundary Conditions (FBC) of reservoir simulators. IFBC algorithm was tested for several sector models of large oil and gas fields. The field size is 50 * 80 km, 4 objects of development with the gas cap, more than 15000 wells, and 44 years of development. 125 regions selected for modeling. Uniform requirements are defined for all sector models. Sector models built for multiple regions of field. The total number of calculated cells is from 7 up to 700 million cells for different implementations of the models. Modeling was done for full model of oil field, for integrated sector models and for non-integrated sector models. Modeling without the integration of sector models leads to errors more than 150% of the accumulated gas cap gas production (FGPTF, WGPTF) and more than 200% for accumulated oil wells (WOPT) in comparison with the full model. Using the algorithm IFBC reduces errors before 2-3%. Computing technology is based on an algorithm IFBC that allows you to create a giant model, "stick together" full of sector models, "implant" sector models in full. Each of the sector models can be created by individual simulator and can have an independent grid.