The energy conversion efficiency of a straight-bladed cross-flow turbine is examined experimentally. The preset pitch angle of the turbine blades is shown to have a large impact on turbine performance for two and four-bladed turbines over the range of tip-speed ratios tested. The optimal preset pitch angle was found to be 6 ◦ for both turbines and nearly all tipspeed ratios. The nominal (apparent) angle of attack in the foil frame of reference is shown to depend only on tip-speed ratio and preset pitch angle if induced velocities are neglected. Turbine performance trends are described via a critical nominal angle of attack, hypothesized to be important during dynamic stall of the foil. Interaction of the foil with a leading edge vortex generated during the dynamic stall process is proposed as an explanatory mechanism for other turbine performance trends. Other hydrodynamic factors possibly influencing turbine performance are discussed briefly.