Upon incorporation of contributions from long-wavelength density fluctuations by a renormalization-group theory, a crossover equation of state is developed for describing thermodynamic properties of chain fluids. Outside the critical region, the crossover equation of state reduces to the classical equation; inside the critical region, it gives nonclassical universal critical exponents. The crossover equation of state correctly represents phase equilibria and pVT properties of chain fluids in both regions. Good agreement is obtained upon comparisons with computer simulations for square-well chain fluids. As obtained from experimental vapor-pressure and density data, the square-well segment-segment parameters for n-alkanes from ethane to eicosane are linear functions of molecular weight. Calculated thermodynamic properties agree well with experiment for n-alkanes from methane to hexatriacontane.