While the relation between code coverage measures and fault detection is actively studied, only few works have investigated the correlation between measures of coverage and of reliability. In this work, we introduce a novel approach to measuring code coverage, called the operational coverage, that takes into account how much the program's entities are exercised so to reflect the profile of usage into the measure of coverage. Operational coverage is proposed as (i) an adequacy criterion, i.e., to assess the thoroughness of a black box test suite derived from the operational profile, and as (ii) a selection criterion, i.e., to select test cases for operational profile-based testing. Our empirical evaluation showed that operational coverage is better correlated than traditional coverage with the probability that the next test case derived according to the user's profile will not fail. This result suggests that our approach could provide a good stopping rule for operational profile-based testing. With respect to test case selection, our investigations revealed that operational coverage outperformed the traditional one in terms of test suite size and fault detection capability when we look at the average results.