The extraction and transportation of bitumen entail energy-intensive and costly methods, necessitating dilution due to its high viscosity. Addressing these challenges requires exploring cost-effective and energy-efficient alternative approaches. Understanding the Liquid-Liquid Equilibrium (LLE) of multicomponent diluent/bitumen systems is crucial to effectively design and optimize oil recovery processes. While the literature provides Vapor-Liquid Equilibrium (VLE) data for these mixtures, there is a significant scarcity of LLE data and predictive models essential for designing and optimizing the mentioned processes. This study presents experimental work on the liquid-liquid equilibrium of CO2/bitumen, a multicomponent natural field gas condensate/bitumen, and a synthetic multicomponent/bitumen. First, phase equilibrium data for CO2/bitumen mixtures are studied over a wide range of pressure (31.59 – 135.99 bar) and CO2 feed concentrations (10 – 70 wt.%) at ambient temperature, with CO2 present in a liquid or dense liquid phase state. Additionally, ethyl acetate (EA) is introduced as a bio-based co-solvent with CO2 to analyze the phase behavior of the system. Second, the study investigates the impact of varying concentrations of multicomponent diluents (ranging from 7 wt.% to 70 wt.%) on the liquid-liquid equilibrium (LLE), density, and viscosity of the multicomponent field natural gas condensate/Mackay River bitumen. Third, the research examines the effects of different concentrations of a multicomponent synthetic solvent (ranging from 5 wt.% to 40 wt.%) on the LLE, density, and viscosity of the synthetic solvent and bitumen mixtures. The studies cover a pressure range of 12.91 – 87.69 bar and a temperature range of 295 – 389 K. The primary thermophysical properties measured include the density and viscosity of the light phase. As part of this study, empirical relationships are established to determine the thermophysical properties of the studied multicomponent systems tools for estimating the density and viscosity of multicomponent diluent/bitumen systems. Additionally, new experimental data are then used to conduct zeroth-order approximation of energy, greenhouse gas emission, and carbon tax recovery analyses of solvent-aided viscosity reduction. LLE measurements of multicomponent/bitumen mixtures are conducted within the temperature range of 295 – 352 K at a constant pressure of 21.59 bar. The Peng-Robinson Equation of State (PR-EoS), the modified Pederson model, and well-established correlations are employed to model the measured density and viscosity data, respectively. A combination of gas chromatography (GC) and gel permeation chromatography (GPC) is utilized for detailed molecular weight and compositional analyses of the heavy and light cuts results from LLE studies. These measurements apply to in-situ bitumen recovery processes and dilbit transportation by pipelines. The outcomes of this study enhance our understanding of the LLE of multicomponent solvent/bitumen systems, providing valuable insights for developing and improving solvent-assisted bitumen transportation and recovery processes and offering promising alternatives to energy-intensive conventional thermal recovery methods.