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 (RI) 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 (RI) 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 (IN); (b) determining the stability reserve by calculating the stability reserve from the solubility blending number (SB o ) and the insolubility number (IN), 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 (RI) 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 (RI) 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 (IN); (i) utilizing the refractive index parameter of the process stream (RI) 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 (IN); (b) determining the stability reserve by calculating the stability reserve from the solubility blending number (SB o ) and the insolubility number (IN), 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. <EOS>