Virtual-electrode catheters and methods for using such virtual-electrode catheters are disclosed. For example, bipolar and multipolar, virtual-electrode catheters having at least one internal electrode and at least one surface electrode, and methods of using these catheters for treatment of cardiac arrhythmias via, for example, radiofrequency (RF) ablation are disclosed. The catheters may comprise a catheter body with an internal lumen extending within it and adapted to flowingly receive a conductive fluid. An exit feature defining a flow path from the internal lumen to the catheter's outer surface may exist through a sidewall of the catheter body. A conductor is mounted within the internal lumen adjacent to the exit feature and is adapted to deliver treatment energy to the tissue via the conductive fluid in the internal lumen. At least one surface electrode is mounted on the outer surface of the catheter body adjacent to the exit feature.