The formulation of thermoplastic materials involves the blending of numerous additives and fillers in order to improve their technical features as well as their processability. The aim of this work is to study the compatibility of functional PE oligomers with polyolefin matrices as they could be used to control the filler dispersion in highly filled polymer formulations. During the blending of a low viscosity oligomer with a high viscosity polymer, the homogenization of the system proceeds through two mechanisms: mixing and diffusion. Several studies have shown that the behaviour of such systems is more sensitive to diffusion than to the viscosity ratio when the latter is lower than 10^-3. Therefore, lubrication occurs in the case of a slow diffusion of the additive into the matrix, causing the low viscosity component to segregate to the high shear rate zones of the mixing equipment. In the present work, bi-layer rheological measurements in molten conditions showed that functional PE oligomers diffuse rapidly into polyolefin matrices. Moreover, rheological characterization of the blends showed a good miscibility between the oligomers and the matrices in the molten state. However, the selected rheological model did not exactly fit the collected data for oligomer concentrations exceeding 10wt%, suggesting the miscibility in such blends could be limited by concentration. Tensile testing of the resulting materials indicated that the presence of an excessive amount of these oligomers could lead to a degradation of the mechanical properties. Differential scanning calorimetry also showed no sign of co-crystallization between the PE oligomers and any of the matrices, suggesting there is a phase separation in the solid state. Furthermore, hot stage optical microscopy and scanning electron microscopy brought some more insight to the study as it confirmed that PE oligomers and some polyolefin matrices form separate domains upon crystallization of the blend.