The production of asphalt cement binder in Iraq is conducted through the distillation of crude oil. The byproduct of such distillation is asphalt cement, which does not practice any further processing. Further processing of the binder is considered vital to controlling its physical properties and chemical composition. The implementation of bio-modifiers before using such asphalt cement binder for paving work is a sound practice to enhance its sustainability and reserve the required rheological properties. In the present study, the asphalt cement binder was modified by the implementation of extender oil (used diesel engine oil) and scrap tire rubber. The aim of this work is to improve and provide a sustainable and proper rheological quality of the binder for paving work. Various percentages of scrap tire rubber and extender oil have been tried to optimize the modifiers that can exhibit a suitable control on the required rheological properties of the asphalt binder, such as the stiffness modulus, its temperature susceptibility in terms of penetration index, and penetration viscosity number, and the temperature of the equivalent stiffness of the binder. The stiffness of asphalt cement binder was digested in hot, moderate, and cold environments. It was observed that the implementation of extender oil was able to reduce the penetration index (PI) by 36.3%, 54.5%, and 27.2% when 15%, 10%, and 5% of extender oil by weight of the mixture were added, respectively, to the control binder. The addition of scrap tire rubber to the binder-oil mixture was able to reduce the PI by up to 10% of the rubber content and exhibited further control over the temperature susceptibility of the binder. It can be revealed that the extender oil increases the negative values of penetration viscosity number (PVN), while the scrap tire rubber can improve the PVN of the binder. When a high percentage of extender oil (15%) is implemented, the stiffness of the binder declines by 50%, 90%, and 75% when the testing temperature changes from 4 to 25, and 60 ℃, respectively. It was concluded that the inclusion of 15% scrap tire rubber and 15% extender oil in the asphalt cement binder produced by Qayarah oil refinery is recommended to provide a sustainable binder for pavement, control its temperature susceptibility, and provide a binder that is less susceptible to pavement distress.