As far as I can tell Google gives no preference to the domain extension when ranking. There a juts a lot more .com names out there, hence may appear hat they rank better.

Some try to argue that a .gov or .edu extension are looked on more favourably than a .com or .net or .info --- I am not convinced as a .edu and .gov are more likely to have a lot of one way incoming links - so they rank better because of that linking and not the domain extension.

CBP