Rheological characteristics of bitumens prepared with process oil Depletion of natural and finite resources has necessitated the worldwide reuse of waste and residue materials from industrial production. Not only does the utilization of crude oil residue with bitumen allow supply of additives at a very low cost, but it also permits the use of waste and residue materials as rejuvenator in nature. The objective of the study is to evaluate conventional and rheological characteristics of original bitumen samples obtained from two different refineries involving different contents (1 %, 2 % and 3 %) of process oil (PO). The results show that PO can be used as an effective and environmentally friendly solution instead of commercially available expensive additives that are used in modification process.