It is important to investigate the equation of state (EoS) in the low density regime which is interesting for heavy-ion collisions. The studies of EoS can provide basic input for the analysis of the experimental signatures for QGP formation. In particular, the chemical potential dependence of EoS may explain the difference of experimental results on freeze-out conditions obtained at different beam energy. We present our recent lattice simulation results for 2-flavor QCD. Derivatives of the thermodynamic grand canonical partition function with respect to chemical potentials for different quark flavors are calculated up to sixth order, enabling estimates of the pressure and the quark number density as well as the chiral condensate and various susceptibilities as functions of the chemical potential via Taylor series expansions. Furthermore, we compare these results to high temperature perturbation theory as well as a hadron resonance gas model.