Compression of long chain fatty acids generates gradients in surface pressure similar to but smaller than those reported previously for polymer monolayers. These have been investigated by reflection spectroscopy and surface pressure measurements for the monolayers at the air/water interface. The gradient increases sharply in the condensed state and is dependent on the chain length of the compounds chosen. The spreading as well as the compression techniques affect the gradient formation and a pressure gradient implying inhomogenity in the monolayer is always present.