Answer: ten
The United States Navy commissioned a total of 10 Nimitz-class aircraft supercarriers during the construction period of that vessel class.
Throughout the 20th century, supercarriers were the largest warships afloat, and represented the impressive warfare superiority of United States Military and Naval Forces.
Nimitz-class supercarriers are identified by the navy designation "CVN". "CV" identifies the ships as being aircraft carriers, and "N" denoting the fact that they are nuclear powered.
The vessel hulls are numbered consecutively, starting with the number 68, and through the number 77.
The 10 supercarriers commissioned by the United States Navy and their home ports (as of 7/1/2009) were:
** CVN-68, USS Nimitz _ _ _ _ _ _ _ _ _ _ _ _ _ San Diego, CA.
** CVN-69, USS Dwight D. Eisenhower _ _ _ _ _ _ Norfolk, VA.
** CVN-70, USS Carl Vinson _ _ _ _ _ _ _ _ _ _ Newport News, VA.
** CVN-71, USS Theodore Roosevelt _ _ _ _ _ _ _ Norfolk, VA.
** CVN-72, USS Abraham Lincoln _ _ _ _ _ _ _ _ Everett, WA.
** CVN-73, USS George Washington _ _ _ _ _ _ _ Yokosuka, Japan
** CVN-74, USS John C. Stennis _ _ _ _ _ _ _ _ Bremerton, WA.
** CVN-75, USS Harry S. Truman _ _ _ _ _ _ _ _ Norfolk, VA.
** CVN-76, USS Ronald Reagan _ _ _ _ _ _ _ _ _ San Diego, CA.
** CVN-77, USS George H.W. Bush _ _ _ __ _ _ _ Norfolk, VA.
Should the need or a threat arise, The United States Navy can respond to any point on the globe within days, bringing a sovereign mobile military combat airport into international waters.
The Nimitz-class supercruisers were unrivaled as far as 20th century military firepower, and could be rapidly deployed.
Supercarrier Tidbit:
The Nimitz-class aircraft supercarrierss were the largest warships ever constructed during the 20th century.
The first ship of this class, USS Nimitz (CVN 68), was commissioned for active duty on May 3, 1975. The 10th and final ship of the class, USS George H.W. Bush (CVN 77), was commissioned for service on January 10, 2009.