A new report has predicted that the number of stores worldwide accepting card payments will double from 46.6 million at the end of 2014 to 90.3 million by 2020.

RBR’s Global Payment Cards Data and Forecasts to 2020 observed that Visa and MasterCard are accepted today by 78% of merchants worldwide but doubted whether both companies will be able to maintain this level, as most of the growth will be in China, where the brands are accepted at only 29 percent of outlets.

Visa and MasterCard are still the most widely accepted payment schemes worldwide, with 37 million outlets each, according to RBR figures. Their numbers are broadly equal in every region, since merchant contracts typically include both.

In the Middle East and Africa, acceptance of Visa and MasterCard is low because neither is currently accepted in the large Iranian market, due to international sanctions. Acceptance of the schemes is also comparatively low in China.

Discover acceptance outside of China is significantly lower than that of Visa and MasterCard. However, as a result of its scheme-to-scheme agreement with UnionPay, Discover’s total worldwide network is nearly the same size. The U.S.-based scheme has similar deals with JCB in Japan and BC Card in South Korea.

UnionPay is the fastest-growing scheme in terms of number of outlets, having increased by 25 percent in 2014 with 5.7 million new outlets. The main driver of this growth is the expansion of the scheme’s home market of China, where it added 4.4 million outlets.

The number of merchant outlets worldwide increased by 17 percent in 2014, with the fastest growth seen in Asia-Pacific followed by central and Eastern Europe.

In these regions, acceptance is expanding from large merchants in cities to include geographic areas and merchant sectors where consumers previously could not use cards.

Already, Asia-Pacific is the largest region in terms of the number of outlets, and RBR is forecasting growth to remain strong until at least 2020. Large but as yet underdeveloped markets such as China and India hold significant potential for further growth. Asia-Pacific currently accounts for 42 percent of global outlets.