Badkar, Mamta. "CHART OF THE DAY: The Skyscraper Index." Business Insider. Business Insider, Inc, 11 Jan. 2012. Web. 31 Mar. 2015
Doherty, Craig A., and Katherine M. Doherty. The Sears Tower. Woodbridge, CT: Blackbirch, 1995. N. pag. Print.
con., April-September................9Am Until 10Pm, October-March..................10Am Until 8Pm, and (Last Entry 30 Minutes Prior To Close).
Www.theskydeck.com Unforgettable.The Best Views Around—into Four States (n.d.): n. pag. Web. "The Infrastructure That Keeps Willis Tower up and
"Out on a Ledge." - Hornall Anderson. N.p., n.d. Web. 31 Mar. 2015.
Running | Willis Tower." The Infrastructure That Keeps Willis Tower up and Running | Willis Tower. N.p., n.d. Web. 30 Mar. 2015. Oxlade, Chris.
Skyscrapers. Chicago, IL: Heinemann Library, 2001. Print. "SOM : Willis Tower (formerly Sears Tower) – Structural Engineering." SOM : Willis Tower (formerly Sears Tower) – Structural Engineering. N.p., n.d. Web. 30 Mar. 2015
"The Willis Tower." The Willis Tower. N.p., n.d. Web. 31 Mar. 2015.
Doherty, Craig A., and Katherine M. Doherty. The Sears Tower. Woodbridge, CT: Blackbirch, 1995. N. pag. Print.
con., April-September................9Am Until 10Pm, October-March..................10Am Until 8Pm, and (Last Entry 30 Minutes Prior To Close).
Www.theskydeck.com Unforgettable.The Best Views Around—into Four States (n.d.): n. pag. Web. "The Infrastructure That Keeps Willis Tower up and
"Out on a Ledge." - Hornall Anderson. N.p., n.d. Web. 31 Mar. 2015.
Running | Willis Tower." The Infrastructure That Keeps Willis Tower up and Running | Willis Tower. N.p., n.d. Web. 30 Mar. 2015. Oxlade, Chris.
Skyscrapers. Chicago, IL: Heinemann Library, 2001. Print. "SOM : Willis Tower (formerly Sears Tower) – Structural Engineering." SOM : Willis Tower (formerly Sears Tower) – Structural Engineering. N.p., n.d. Web. 30 Mar. 2015
"The Willis Tower." The Willis Tower. N.p., n.d. Web. 31 Mar. 2015.