The Integral Equation Theory (IET) of fluids and molecular dynamics (MD) simulations have been used to study the stability and aggregation of asphaltenes in asphaltene-resin mixtures with different host solvents (n-heptane, toluene, and pyridine). The theory is based on an approximate interaction-potential model that represents the asphaltene-asphaltene (A-A), asphaltene-resin (A-R), and resin-resin (R-R) interactions in a solvent of dielectric constant c. This interaction potential is used within the Ornstein-Zernike Hypernetted Chain (OZ-HNC) approximation for calculating radial distribution functions, structure factors, the limits of material stability, and the phase diagrams of asphaltene-containing systems, where the peptizing behavior of resins is studied as a function of the ratio of resin-to-asphaltene molecules in each host solvent. Comparisons of the theoretical OZ-HNC and MD simulations confirm the good accuracy of the proposed approach, which suggests its suitability as an alternative calculation method for predicting the phase behavior of asphaltene-containing oil fluids.