KC-X is the internal name for the United States Air Force's next generation aerial refueling tanker aircraft. This aircraft will replace the Boeing KC-135, which has been in service since 1957. The DoD posted a request for proposal on January 30, 2007.
The U.S. Air Force's main requirements are "fuel offload and range at least as great as the KC-135", airlift capability, ability to take on fuel in flight, and multi-point refueling capabilty.
There have been, so far, two manufacturers that have expressed interest in producing this proposed aircraft:
- A joint venture between EADS/Airbus and Northrop Grumman to produce a version of the Airbus A330 Multi Role Tanker Transport (MRTT), based on the Airbus A330
- Boeing, to produce a version of the KC-767, based on the Boeing 767
Both of these aircraft have been ordered by other nations, but not yet delivered to their respective customers.
The KC-X is the name being used until the design and vendor are selected. The aircraft will then be given an official designation pursuant to the DoD aircraft designation system. The DoD is anticipating that this aircraft will start to enter service in 2013.
One comparison of the aircraft notes, "Northrop has been viewed as the underdog, with a heavier, less fuel efficient aircraft. Northrop spokesman Randy Belote said Northrop's K-30 would tack on roughly 20 percent in fuel capacity." 
- Air Force Posts Request for Proposals for Tankers. United States Department of Defense. Retrieved on 2007-02-16.
- Northrop Grumman KC-30 marketing web site. Northrop Grumman. Retrieved on 2007-02-16.
- Boeing Offers KC-767 Advanced Tanker to U.S. Air Force. Boeing (2007-02-12). Retrieved on 2007-02-16.
- KC-X Advanced Mobility Aircraft. GlobalSecurity.org. Retrieved on 2007-02-16.
- Borak, Donna (2007-02-13). Boeing Tweaks 767 for Tanker. The Seattle Times. Retrieved on 2007-02-23.
- Future Strategic Tanker Aircraft; British tanker procurement program.