Open access publishing (OAP) makes research output freely available, and several national governments have now made OAP mandatory for all publicly funded research. Gold OAP is a common form of OAP where the author pays an article processing charge (APC) to make the article freely available to readers. However, gold OAP is a cause for concern because it drives a redistribution of valuable research money to support open access papers in ?mega-journals? with more permissive acceptance criteria. We present a data-driven evaluation of the financial ramifications of gold OAP and provide evidence that gold OAP in mega-journals is biased toward Western industrialized countries. From 2011 to 2015, the period of our data collection, countries with developing economies had a disproportionately greater share of articles published in the lower-tier mega-journals and thus paid article APCs that cross-subsidize publications in the top-tier journals of the same publisher. Conversely, scientists from Western developed countries had a disproportionately greater share of articles published in those same top-tier journals. The global inequity of the cross-subsidizing APC model was demonstrated across five different mega-journals, showing that the issue is a common problem. We need to develop stringent and fair criteria that address the global financial implications of OAP, as publication fees should reflect the real cost of publishing and be transparent for authors.