Large publishing companies have been dominating scientific publishing for long, which leads to high subscription fees and inhibited access to scientific knowledge. At digital era, the opportunity of an unrestricted access appears feasible, because the cost of publishing should be low. It is no longer the readers and libraries to pay subscription fees, but scientific organizations and authors themselves who pay for the cost of having their article published. As the data shows, there is a tremendous variance of article processing charges (APC) across journals, which obviously cannot be explained by the costs. One of the explanatory variables could be reputation, but it only contributes less than 5% to the variance in average APC. This study is meant to shed light on the various determinants of APC. Based on the data from the OpenAPC Initiative, the Directory of Open Access Journals and three different datasets of Web of Science, we employ ANOVAs and multivariate regressions. The results show that market power plays an important role to explain APC, inter alia, through market concentration, market position of individual publishers (publisher size), and the choice of hybrid publishing model.