The density of liquid iron sulfide (FeS) was measured up to 3.8 GPa and 1800 K using an X-ray absorption method. The compression curve of liquid FeS was fitted using the Vinet equation of state. The isothermal bulk modulus and its temperature and pressure derivatives were determined using a nonlinear least-squares fit. The parameter sets determined were: K0T = 2.5 ± 0.3 GPa at T = 1500 K, (dK0/dT)P = −0.0036 ± 0.0003 GPa/K, and (dK0/dP)T = 24 ± 2. These results suggest that liquid FeS is more compressible than Fe-rich liquid Fe-S.