There is a new SimCity Insider blog published on SimCity.com that talks about the new online Global Market. The new Global Market in SimCity is based on player activity and is similar to that of a stock market that changes the prices of goods within cities.
One of the many new features in SimCity is the online Global Market. The Global Market can be thought of as a shared stock market that tracks the prices of the several resources we have in the game. The prices of resources are not fixed, but are based on player-driven market activity. If more cities are selling than buying, then the prices of goods will drop. Conversely, the price will rise if the buyers outnumber the sellers.
Thanks to TheSimsHub for the tip.