Chicago is an international hub for finance, culture, commerce, industry, technology, telecommunications, and transportation. It is the site of the creation of the first standardized futures contracts at the Chicago Board of Trade, which today is the largest and most diverse derivatives market globally, generating 20% of all volume in commodities and financial futures. O'Hare International Airport is one of the busiest airports in the world, and the region also has the largest number of U. S. highways and greatest amount of railroad freight. In 2012, Chicago was listed as an alpha global city by the Globalization and World Cities Research Network, and it ranked seventh in the entire world in the 2017 Global Cities Index. The Chicago area has one of the highest gross domestic products (GDP) in the world, generating $680 billion in 2017. In addition, the city has one of the world's most diversified and balanced economies, not being dependent on any one industry, with no single industry employing more than 14% of the workforce.