Carbon black (CB) is essentially carbon in the form of extremely fine particle aggregates (100-200nm) having an amorphous molecular structure. Oil absorption or compressed dibutyl phthalate (CDBP) and iodine adsorption or nitrogen surface area (N2SA) are parameters commonly used to describe CB morphology or structure and the surface area of CB available for reaction with rubber. We have used both positron lifetime and Doppler broadening spectroscopy to study these two parameters for a variety of rubber CB composite samples. The o-Ps pickoff lifetime depends only on the type of rubber and is independent of CDBP and N2SA. However, the o-Ps lifetime intensity, I3, and the S parameter decrease with both CDBP and N2SA.