Many studies have shed light on the positive side of relatedness, but little attention has yet been devoted to possible downsides of relatedness for firm performance in regions. We found in a case study of the oil-dependent Stavanger region in Norway that plants in industries that are skill-related to the dominant oil and gas industry showed lower employment growth than plants in other industries. This was the case both in the boom and the crisis periods, even when controlling for supply linkages to the oil and gas sector. However, we also found that plants skill-related to the oil and gas industry increased their relative performance during the crisis to some degree, but they did not outperform the non-skill-related plants during the crisis.