Our experimental observations demonstrate an enhancement of the cis conformer abundance of CH3ONO upon matrix isolation that has not been identified previously. Our systematic study of the angular and host dependances of the observed isomer abundances implicates gas/surface interactions during the deposition process as being responsible for this enhancement. We conclude that enhancement of the cis conformer is due to a competition between energetic stabilization of cis and enhanced surface trapping of cis due to its smaller van der Waals radius.