The pricing of low-cost carriers (LCCs) compared with traditional airlines has been extensively investigated since their inception in the air transport market. Abundant empirical evidence attests that, on average, LCCs' fares (per km) are lower than those usually offered by full-service carriers (FSCs). Such literature, however, paid virtually no attention to the conditions under which LCCs lose their convenience compared to traditional airlines. The purpose of this study is to investigate the occurrence of LCCs sometimes offering higher fares than FSCs on competing flights. By using a dataset expressly collected for this purpose, we are able to quantify its frequency and suggest some possible explanations. These findings concur to cast some questions on the widely held preconception of vertical differentiation between LCCs' and FSCs’ offered services. Further research will be needed in order to understand the relative weight of the suggested factors.