Removal of asphaltenes from heavy oil improves the quality of oil and makes it easier to process. In the current work, in situ prepared NiO and Fe2O3 nanoparticles within heavy oil, display much higher affinity towards asphaltenes adsorption than commercial ones. Nanoparticle preparation followed a method developed by our group and XRD, EDX and TEM analyses confirmed the formation of NiO nanoparticles of 125 nm and Fe2O3 nanoparticles of 36±5 nm mean diameter. Kinetic experiments showed that, while equilibrium could be achieved in less than 2 h for both in-situ prepared and commercial NiO particles, much higher adsorption took place onto the in-situ prepared ones, owing to their better dispersion. An uptake in the order of 2.8 and 2.7 g asphaltenes/g nanoparticles was reported for in-situ prepared NiO and Fe2O3 nanoparticles, respectively. Commercial NiO and Fe2O3 nanoparticles of the same size range and subject to the same experimental conditions only adsorbed 15% and 25% of the above values, respectively. Degassing temperature was found to have a major effect on the surface area. For in situ prepared Fe2O3, surface area evaluated by BET method following degassing the sample at 200oC was found to be significantly lower than the one evaluated at 300oC. SEM analysis for non-heat treated and heat treated, at 300°C, in-situ prepared Fe2O3 showed that heat treatment caused more resolution and provided more definition of the capped nanoparticles with the agglomerated cluster. The difference between the heat treated and non-heat treated samples supports the adsorption model in which hydrocarbons were adsorbed onto the nanoparticles and not vice versa. Monolayer adsorption on the nanoparticles was reported from the toluene model solutions. Contrary to literature findings on adsorption from model solutions onto nanoparticles, our results support a model of sequential oxidation of adsorbed asphaltenes and multilayer adsorption of asphaltenes from heavy oils onto in-situ prepared and commercial NiO nanoparticles. The thermal behavior of the multilayered asphaltenes suggests new interpretation of the role of the nanoparticles.