Below is a list of stocks that are traded on three exchanges: the New York Stock Exchange (NYSE), the Hong Kong Stock Exchange (HKEX), and the Shanghai Stock Exchange (SSE). As you will notice, there is a premium ranging from 12% to 388% for stocks listed in Shanghai compared to those listed in the US for the same company. In a market where there are no restrictions on supply and demand and no easy arbitrage opportunities, there probably would still be a difference in the pricing of a stock that is listed on two different exchanges. It is an issue I'd be interested in looking into. According to this article, from the 45 Chinese companies dual-listed in both Hong Kong and the mainland, the H-shares are 34% cheaper. Recently, there was a rumor from the China Securities Regulatory Commission (CSRC) that suggested the PRC was considering allowing swaps between the A-shares listed on the mainland and the H-shares listed in Hong Kong. Although these rumors were later dismissed, it certainly raises questions such as how efficient the SSE and HKEX currently are and also what the equilibrium prices would be if these swaps were allowed.