The building was part of the later
Rockefeller Center expansion (1960s–1970s) dubbed the
"XYZ Buildings". Their plans were first drawn in 1963 by the
Rockefeller family's architect,
Wallace Harrison, of the architectural firm
Harrison & Abramovitz. Their letters correspond to their height. 1251 Avenue of the Americas is the "X" Building as it is the tallest at 750 ft (229 m) and 54 stories, and was the first completed, in 1971. The "Y" is
1221 Avenue of the Americas, which was the second tower completed (1973) and is the second in height (674 ft and 51 stories). The "Z" Building, the shortest and the youngest, is
1211 Avenue of the Americas with 45 stories (592 ft). 1251 is the second-tallest building in the whole of Rockefeller Center, after
30 Rockefeller Plaza. Despite being one of the 100
tallest buildings in the United States, 1251 Avenue of the Americas is almost impossible to see from more than just a few blocks away as it is flanked on all sides by buildings over 500 feet tall. The result is that even though 1251 Avenue of the Americas is approximately as tall as the tallest buildings in cities such as
Boston or
Minneapolis, it has almost no presence on the
New York City skyline. In 1989,
Exxon announced that it was moving its headquarters and around 300 employees from
New York City to the
Las Colinas area of
Irving, Texas. Exxon sold the Exxon Building, its former headquarters, to a unit of
Mitsui Real Estate Development Co. Ltd. in 1986 for $610 million. John Walsh, president of Exxon subsidiary Friendswood Development Company, stated that Exxon left New York because the costs were too high. Its New York offices moved to
Brooklyn; it no longer retains a presence in Rockefeller Center. In May 2013, the structure received silver certification under the
U.S. Green Building Council's
LEED for Existing Buildings Rating System. ==Art==