[en] In recently publicized cold fusion experiments at the University of Utah, generation of excess heat was reported. To investigate mechanisms that may contribute to energy flows in electrolysis cells, a series of experiments was performed at the Idaho National Engineering Laboratory (INEL). Ordinary water (H₂O), heavy water (D₂O), and mixture of the two were used in the INEL experiments. Cathodes used include a 51-μm Pd foil and 1-mm diameter extruded wire Pd rods in two configurations. Energy balances in these experiments revealed that some of the required voltage to sustain a given current is due to irreversibilities associated with cell operation. Particularly significant are electrolyte resistance and activation energy polarization effects. Energy balances in the INEL experiments showed there was no significant net grain or net loss of energy. Cell overpotential curves were fit well with a Tafel equation, with parameters dependent on electrode configuration, electrolyte composition, and temperature. Water evaporation and interactions of hydrogen isotopes with the Pd cathode were evaluated and found not to be significant to energy balances. No ionizing radiation, tritium production, or other evidence of fusion reactions was seen in the INEL experiments. 4 refs., 6 figs., 2 tabs