A method of determining solubility parameters and stability reserve of a process stream containing asphaltenes, the method comprising: (a) determining the solubility parameters by measuring: - a refractive index parameter of the process stream, - a refractive index parameter at the flocculation onset of the asphaltenes (RI 0), wherein the flocculation onset is determined via turbidimetric titration, and - a refractive index parameter (RI a) of an asphaltenic solution formed by redispersing the precipitated asphaltenes recovered at the flocculation onset in a solvent, wherein the measuring comprises: (i) utilizing the refractive index parameter of the process stream as a direct measurement of a solubility blending number (SB 0); (ii) utilizing the refractive index parameter at the flocculation onset of the asphaltenes (Ri 0) as a direct measurement of the insolubility number; and (iii) converting the refractive index parameter (RI a) into a solubility blending number (SB a) of the precipitated asphaltenes; (b) determining the stability reserve by calculating the stability reserve as the ratio of the solubility blending number (SB 0) to the insolubility number; and characterised in further comprising step (c) making a measurement of the stabilizing/solvating role of resins in the process stream fluid on the asphaltenes, wherein the difference in the solubility parameter of the asphaltenes precipitated at the flocculation onset and the solubility parameter of the process stream with precipitant at the flocculation onset (SB a -IN) is indicative of the stabilizing/solvating effect of the resins on the asphaltenes. (a) determining the solubility parameters by measuring: - a refractive index parameter of the process stream, - a refractive index parameter at the flocculation onset of the asphaltenes (RI 0), wherein the flocculation onset is determined via turbidimetric titration, and - a refractive index parameter (RI a) of an asphaltenic solution formed by redispersing the precipitated asphaltenes recovered at the flocculation onset in a solvent, wherein the measuring comprises: (i) utilizing the refractive index parameter of the process stream as a direct measurement of a solubility blending number (SB 0); (ii) utilizing the refractive index parameter at the flocculation onset of the asphaltenes (Ri 0) as a direct measurement of the insolubility number; and (iii) converting the refractive index parameter (RI a) into a solubility blending number (SB a) of the precipitated asphaltenes; - a refractive index parameter of the process stream, - a refractive index parameter at the flocculation onset of the asphaltenes (RI 0), wherein the flocculation onset is determined via turbidimetric titration, and - a refractive index parameter (RI a) of an asphaltenic solution formed by redispersing the precipitated asphaltenes recovered at the flocculation onset in a solvent, wherein the measuring comprises: (i) utilizing the refractive index parameter of the process stream as a direct measurement of a solubility blending number (SB 0); (ii) utilizing the refractive index parameter at the flocculation onset of the asphaltenes (Ri 0) as a direct measurement of the insolubility number; and (iii) converting the refractive index parameter (RI a) into a solubility blending number (SB a) of the precipitated asphaltenes; (i) utilizing the refractive index parameter of the process stream as a direct measurement of a solubility blending number (SB 0); (ii) utilizing the refractive index parameter at the flocculation onset of the asphaltenes (Ri 0) as a direct measurement of the insolubility number; and (iii) converting the refractive index parameter (RI a) into a solubility blending number (SB a) of the precipitated asphaltenes; (b) determining the stability reserve by calculating the stability reserve as the ratio of the solubility blending number (SB 0) to the insolubility number; and characterised in further comprising step (c) making a measurement of the stabilizing/solvating role of resins in the process stream fluid on the asphaltenes, wherein the difference in the solubility parameter of the asphaltenes precipitated at the flocculation onset and the solubility parameter of the process stream with precipitant at the flocculation onset (SB a -IN) is indicative of the stabilizing/solvating effect of the resins on the asphaltenes.