Oxygen solution in Fe-Ni-Cr melts containing manganese, silicon, and aluminum has been thermodynamically analyzed and experimentally studied at 1873 K (1600 °C). The Fe-10 pctNi-20 pctCr and Fe-40 pctNi-15 pctCr compositions were studied as examples of the most frequently used alloys. Manganese is not a deoxidizer in these alloys, since manganese and chromium have similar affinities for oxygen. At low contents, silicon is also not a deoxidizer. However, above 0.358 pct for the Fe-10 pctNi-20 pctCr alloy and 0.261 pct for the Fe-40 pctNi-15 pctCr alloy, silicon decreases the oxygen concentration in the melts. Aluminum is an effective deoxidizer in the Fe-Ni-Cr melts. It decreases the oxygen concentration when its content is higher than 2.914 × 10−4 pct in the Fe-10 pctNi-20 pctCr alloy and 2.109 × 10−3 pct in the Fe-40 pctNi-15 pctCr alloy. Minimum oxygen concentrations are observed at aluminum contents of about 0.24 pct in the Fe-10 pctNi-20 pctCr alloy and at about 0.23 pct in the Fe-40 pctNi-15 pctCr alloy. The combined deoxidation of Fe-10 pctNi-20 pctCr and Fe-40 pctNi-15 pctCr alloys with silicon and manganese and also with aluminum and silicon was studied. The lower oxygen concentrations were reached as a result of complex deoxidation in comparison with the cases when deoxidized separately by each element at the same concentration levels.