Zero-rating means that when using the (mobile) Internet, the data traffic for certain services or applications (apps) does not count towards a tariff’s data cap. It is a practice used by several mobile telephony operators in the European Union. As of today, there are hardly any empirical studies on the effects of zero-rating. In this study we analyse tariffs of 53 mobile network operators in 15 EU countries over the period 2015-2018 in order to investigate the effects of zero-rating on data caps, monthly prices and prices per unit of included data.