A theoretical study of filtration characteristics of rectangular electret fibers arranged in a staggered array perpendicular to the flow direction was conducted assuming the Brownian diffusion and interception as the dominant particle capture mechanisms. The single-electret fiber efficiency due to pure diffusion was found to be proportional to -2/3, 0.278, and 1/2 powers of the Peclet number (based on the fiber hydraulic diameter), filter solid-volume fraction, and fiber aspect ratio, respectively. For pure interception, the single fiber efficiency was determined to be proportional to 1.55 and 0.54 powers of the interception parameter and filter solid-volume fraction, respectively. This is Particle Technology Laboratory Publication No. 741.