The Aon Center (200 East Randolph Street, formerly Amoco Building)[3] is a modern supertall skyscraper located in the Northeast corner of the Chicago Loop, Chicago, Illinois, United States, designed by architect firms Edward Durell Stone and The Perkins and Will partnership, and completed in 1973[4] as the Standard Oil Building (nicknamed "Big Stan").

When completed, it was the world's tallest marble-clad building, sheathed entirely with 43,000 slabs of Italian Carrara marble.

[5][15] Amoco was reluctant to divulge the actual amount, but it was well over half the original price of the building, without adjustment for inflation.

Under a grant from the Illinois Department of Rehabilitative Services, Regalo's 25 handicapped workers carved the discarded marble into a variety of specialty items such as corporate gifts and mementos including desk clocks and pen holders.

[5][16] The building's facade somewhat resembles that of the North and South tower of the former World Trade Center Complex due to the upward flow of the columns.

[1] On May 14, 2018, the building's owners unveiled a $185 million proposal for an observatory featuring a thrill ride on the roof called the Sky Summit, the world's tallest exterior elevator, and new entrance pavilion.