The difficulties of achieving the necessary accuracy in counts of criminal opportunities derive in large part from the conceptual complexities; opportunity is not merely the necessary condition for offending, but it can provoke crime and can also be sought and created by those with the necessary motivation. The benefits of refinement are considerable; these relate not just to documenting the infrequency of crime but also to some of the other purposes served by opportunity-based crime rates; and, because of the great variety of crime, it would usually be necessary to have a variety of data about ratios of crime to opportunity. To properly explain historical or international differences in crime, it may be necessary to measure opportunity in different ways, not just in relation to the availability of material goods but also to the means of committing crime and to patterns of work and leisure. While situation-based ratios of crime to conformity might have a particular value in denoting potential scope for preventative action, target-based measures might be a better guide to its precise form. Finally, while all attempts to measure more accurately the ratio of crime to opportunities may have the desirable effect of directing theorists to pay as much attention to conformity as to deviance, a variety of data about these ratios would also force them to accord a greater role to the circumstances and conditions under which different forms of crime take place. A total of 36 references are included. (Author summary modified)