Viscfac 4 = 0.5354 × Viscfac 3 -0.1170 (28) as terms that take into account a temperature dependence for the oil average molecular weight. We highlight that this term is not present in Lindeloff et al. work, but it is considered in Pedersen et al.. The equation 24 is applied only in atmosphere pressure conditions. To capture the pressure effects, the following correction is employed η heavy = η oil exp 0.00384 P 0.8226 -1 0.8226 (29) for viscosities in cP and pressures in atm. In summary, to estimate mixture viscosity, the classical CSP model is applied for methane reference temperatures greater than 75 K. For reference temperatures < 50 K, the modified heavy oil model described above is used. And, for temperatures between 50 K and 75 K, the reference viscosity is calculated as a smooth transition with respect to each model as follows