Since NATO was founded in 1949, the issue of burden-sharing has been fiercely debated. Members have argued about what constitutes a fair contribution and who is getting the most benefit. During the early days, America’s monopoly on nuclear weapons led to U.S. overcontribution and free riding by the poorer members. After NATO moved to a flexible response military strategy, conventional weapons became more relevant and burden-sharing came to be more balanced. Since the 1992 Oslo declaration committed the alliance to out-of-area crisis response, burden-sharing has changed again. Using the NATO air operations in the Balkans conflict as a case study, I show that burden-sharing has again shifted towards exploitation of wealthier members. Rather than using military expenditures as a contribution measurement, I examine aircraft and sortie contributions to the combat operations. Based on a Spearman rank correlation test using aircraft contributions, I find evidence that the rich carried a disproportional burden in the conflict. The exploitation was more pronounced when I examined the sorties flown by each nation, showing that the richer members flew their aircraft disproportionately more than the poorer ones. Examining contributions of the more complex and expensive support aircraft resulted in even stronger evidence of exploitation. In addition, the U.S. became an extreme outlier when I examined the sorties flown by these support aircraft. No other member was able to provide these critical types of sorties. These results endorse the argument that a capabilities gap exists in NATO. When I compared these defense burdens to benefit measurements, I find a lack of concordance between burdens and benefits during the Kosovo air campaign. Many European members received a larger benefit share relative to their aircraft and sortie contributions to the conflict. This suggests less cohesion in the alliance. Analysis of the contributions of support aircraft and sorties provided the strongest evidence of a three-tiered alliance with burden and benefit shares significantly out of balance. The emergence of the capabilities gap indicates that the alliance will face significant policy challenges moving forward.