To study the possibility of overdoping with oxygen and, thus, an increase in the charge carrier density, nH(100 K), in RE123 layers (RE Eu, Gd) with the aim of increasing the critical current density, Jc, oxygenation was carried out in the pressure range of pO2 1160 bar and temperatures of TS 300800 C during 312 h of commercial EuBCO and GdBCO coated conductors (CC), from which the protective Cu layer and, in half of the cases, the Ag layer were chemically removed before oxygenation. The evidences of overdoping were observed about what were witnessed an increase of nH(100 K), reduction of c-lattice parameters of RE123 (RE Eu, Gd) of superconducting layers, behavior of normalized resistivity before superconducting transition, and Jc variation, however, the conditions to achieve optimal doping were not found yet. Treatment under 100 bar of O2 for 3 h of GdBCOCC (with Ag layer) at 600 C led to an increase in Jc (77 K, 0 T) from 2.57 to 2.67 MAcm2, nH(100 K) increased from 6.55 1021 to 6.91 1021 cm3, and Jc(5 K, 0 T) 28.94 MAcm2 was observed after the treatment. The increase in Jc (77 K, 0 T) from 2.10 to 2.28 MAcm2 for GdBCOCC (without Ag layer) was observed after treatment at 300 C under 100 bar of O2 for 3 h. In the both cases c-parameter of Gd123 decreased from 1.1735(1) to 1.1731(0) nm. For EuBCO after treatment a decrease in c-parameters of Eu123 was observed: from 1.1738(8) to 1.1734(5) nm (for the Ag-coated sample under 100 bar O2 at 300 C) and from 1.1740(2) to 1.1736(3) nm (for the sample without Ag under 160 bar O2 at 800 C), but we failed to increase nH(100 K) and Jc of the studied samples. However, the studies are still ongoing.