How do you check thermodynamic consistency of VLE data?

Thermodynamic consistency tests verify that experimental VLE data satisfies fundamental relationships. Area test (Redlich-Kister): integral of ln(gamma_1/gamma_2) vs x should equal zero for consistent data. Point test: verify activity coefficients satisfy Gibbs-Duhem equation (sum of x_i*d_ln_gamma_i = 0 at constant T, P). Herrington test: modified area test with temperature correction. Inconsistent data may indicate experimental errors, impure components, or incomplete equilibration. Consistency checking is essential before using data for parameter fitting.