The Aon Center is a modern skyscraper in the Chicago Loop, Chicago, Illinois, United States, designed by architect firms Edward Durell Stone and The Perkins and Will partnership, and completed in 1973 as the Standard Oil Building. With 83 floors and a height of 1,136 feet (346 m), it is the third tallest building in Chicago, surpassed in height by the Willis Tower and the Trump International Hotel and Tower. The building is managed by Jones Lang LaSalle. Aon has the headquarters of the Aon Corporation, and it formerly had the headquarters of Amoco. The Aon Center is almost identical in design and floorplan to First Canadian Place in Toronto, Canada, the only major design difference being the orientation of the exterior windows.
The Standard Oil Building was constructed as the new headquarters of the Standard Oil Company of Indiana, which had previously been housed at South Michigan Avenue and East 9th Street. When it was completed in 1973 it was the tallest building in Chicago and the fourth-tallest in the World, earning it the nickname "Big Stan". (A year later, the Sears Tower took the title as Chicago's and world's tallest.) The building employs a tubular steel-framed structural system with V-shaped perimeter columns to resist earthquakes, reduce sway, minimize column bending, and maximize column-free space. This construction method was also used for the World Trade Center towers in New York City.