The article analyses empirically four methods of measuring willingness to pay (WTP), i.e., directly stated WTP, indirectly stated WTP (employing conjoint analysis), first price auction and Vickrey auction. The sample consists of 1,089 respondents and more than 3,000 individually measured WTP regarding 100 phone minutes for sale. As one result we found that the measured WTP differs significantly and also substantially between different methods. Furthermore, interviews without purchase obligation, i.e., hypothetic questions, have a clear hypothetical bias. The theoretical advantageousness of Vickrey auctions cannot be confirmed.