Simulations of various GLAO systems for telescopes up to 32 meter are presented. We have generated point spread functions of several GLAO configurations using ESO's parallel simulation tool and compared the results with analytically computed PSFs. A good agreement is observed when simulating bright guide stars (both LGSs and NGSs) although the analytical approach does not consider for instance wavefront sensor errors or servo lag. Other more realistic configurations (asymmetrically located and dim guide stars) are investigated and the need for advanced control methods in such cases are considered.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.