We analyze the extraordinary transmission effect in the periodic and random nanoaperture arrays in optically thick metal films. Experimental studies are combined with simulations to show that extraordinary transmission effect at midinfrared wavelengths is enhanced when the decaying waveguide mode of a single nanoaperture couples through the collective surface plasmon excitations created through periodicity. Transmission characteristics of the individual nanoapertures are investigated by randomizing the apertures. By comparing rectangular to coaxial rectangular nanoapertures, both of which support TE(01)-like decaying waveguide modes, we study the effect of nanoaperture geometry on the efficiency of the transmission. (C) 2008 American Institute of Physics.