This paper attempts to quantify the effects of array layout on the performance of offshore wind farms. Array layout is characterized by the spacing between wind turbines (along and across the prevailing wind direction) and by their alignment (aligned or staggered). A large-eddy simulation code is utilized to create a turbulent boundary layer and is coupled with an actuator line model to simulate the effects of the rotating wind turbine blades. A control case (simulating the Lillgrund farm) and sensitivity runs are performed with various combinations of increased spacing, with and without staggering. Staggering every second row was found to be the simplest method to improve the capacity factor from 0.3 to 0.34 and array losses from 36% to 27%. The highest capacity factor (0.4) and the lowest array losses (14%) were obtained with a staggered layout with spacing across the prevailing wind direction that was twice the original. Smart layout choices can improve the array performance by 13%-33%.