The effects of additives in various vegetable oils on the physical, mechanical, and adhesion properties of carbon black/rubber compounds were studied. Various doses of castor oil and some other oils such as paraffin oil, vegetable oil 1, and cashew nut shell liquid (CNSL) at a fixed dose (1 phr) were used. With an increase in the castor oil content, the modulus, tear strength, and tensile strength increased, whereas the hardness and adhesive strength exhibited little variation up to 1 phr. Beyond 1 phr castor oil, the modulus, tear strength, and hardness decreased, whereas the adhesive and tensile strengths increased up to 2.5-3 phr and then decreased. Therefore, castor oil seemed to behave as a coupling agent up to 1 phr and as a coupling agent and a plasticizer in the range of 1-3 phr; beyond that, the main role of castor oil was plasticization. When various oils at a fixed dose (1 phr) were compared, it was found that the vegetable oils exhibited enhanced properties in comparison with those of paraffin oil. In addition, both of the unsaturated oils (castor oil and vegetable oil 1) enhanced physical and mechanical properties in comparison with saturated paraffin oil. CNSL exhibited the best adhesion properties against mild steel and galvanized iron substrates.