We report here, for the first time, evolution of the streaming potential coupling coefficient as liquid carbon dioxide infiltrates Berea sandstone. Using 125 Ω-m tap water, the coupling coefficient determined before and after each CO2 flood of five samples averaged approximately −30 mV/0.1 MPa. After liquid CO2 passed through the specimens displacing all mobile pore water, trapped water remained and the coupling coefficient was approximately −3 mV/0.1 MPa. A bound water limit of the coupling coefficient for liquid CO2 flow was found using an air-dried sample to be −0.02 mV/0.1 MPa. For initially water-saturated samples, bulk resistivity varied during CO2 invasion from 330 Ω-m, to 150 Ω-m during CO2/water mixing, to a final value of 380 Ω-m. Results suggest that trapped and bound water control electrical conduction and the electrokinetic response. Applications include monitoring CO2 injectate in subsurface reservoirs using the self potential method.