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 and a refractive index parameter at the flocculation onset of the asphaltenes (RI o), wherein the flocculation onset is determined via turbidimetric titration, and wherein the measuring comprises: (i) utilizing the refractive index parameter of the process stream as a direct measurement of a solubility blending number (SB o); and (ii) utilizing the refractive index parameter at the flocculation onset of the asphaltenes (RI o) as a direct measurement of the insolubility number; (b) determining the stability reserve by calculating the stability reserve from the solubility blending number (SB o) and the insolubility number, wherein the stability reserve is the ratio of the solubility blending number to the insolubility number; and characterised in that the method further comprises: (c) recovering precipitated asphaltenes at the flocculation onset, redispersing the precipitated asphaltenes in a solvent to form an asphaltenic solution, measuring the refractive index parameter of the asphaltenic solution (RI a), and converting the refractive index parameter (RI a) into a solubility blending number (SB a) of the precipitated asphaltenes; wherein a 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 used to calculate the stabilizing/solvating effect of resins on the asphaltenes; and wherein the process stream comprises a live crude oil. (a) determining the solubility parameters by measuring a refractive index parameter of the process stream and a refractive index parameter at the flocculation onset of the asphaltenes (RI o), wherein the flocculation onset is determined via turbidimetric titration, and wherein the measuring comprises: (i) utilizing the refractive index parameter of the process stream as a direct measurement of a solubility blending number (SB o); and (ii) utilizing the refractive index parameter at the flocculation onset of the asphaltenes (RI o) as a direct measurement of the insolubility number; (i) utilizing the refractive index parameter of the process stream as a direct measurement of a solubility blending number (SB o); and (ii) utilizing the refractive index parameter at the flocculation onset of the asphaltenes (RI o) as a direct measurement of the insolubility number; (b) determining the stability reserve by calculating the stability reserve from the solubility blending number (SB o) and the insolubility number, wherein the stability reserve is the ratio of the solubility blending number to the insolubility number; and (c) recovering precipitated asphaltenes at the flocculation onset, redispersing the precipitated asphaltenes in a solvent to form an asphaltenic solution, measuring the refractive index parameter of the asphaltenic solution (RI a), and converting the refractive index parameter (RI a) into a solubility blending number (SB a) of the precipitated asphaltenes; wherein a 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 used to calculate the stabilizing/solvating effect of resins on the asphaltenes; and wherein the process stream comprises a live crude oil.