Are OEF, OIF, and ISAF different theaters of operations?

OIF and OEF are two missions which both fall under the Global War on Terrorism.
ISAF is the NATO led International Security Assistance Force which is tasked with the security mission in Afghanistan.

Theater: "The geographical area for which a Commander of a Geographic Combatant Command has been assigned responsibility. Combatant Command: "A unified or specified command with a broad continuing mission under a single commander established and so designated by the President, through the Secretary of Defense and with the advice and assistance of the Chairman of the Joint
Chiefs of Staff." Specified Combatant Command: "A command, normally composed of forces from a single Military Department, that has a broad, continuing mission, normally functional, and is
established and so designated by the President through the Secretary of Defense with the
advice and assistance of the Chairman of the Joint Chiefs of Staff." Unified Command: "A command with a broad continuing mission under a single commander and composed of significant assigned components of two or more Military Departments that is established and so designated by the President, through the Secretary of Defense with the advice and assistance of the Chairman of the Joint Chiefs of Staff. Also called unified combatant command." So...from this...we must do what is always done with doctrine. We have to piece it together. When the Joint Community talks about GCC's, we talk about CENTCOM, SOUTHCOM, PACOM, NORTHCOM, EUCOM, etc. These are our Geographic Combatant Commands. Thus, a Theater would be that geographic area of operations which they are responsible for. Using this definition, we see that the ones you are referencing are in CENTCOM...ONE THEATER. That being said, there used to be a Unified Command in Iraq. I don't know if it's still there. USF-I used to be a Unified Command. You could argue that at that time, Iraq was its own Theater under that Unified Command. The Commander received support and assistance from CENTCOM, but had a direct line to the Secretary of Defense, much like the CENTCOM commander does. I don't know if the same thing can be said about Afghanistan. As pointed out, OIF and OEF are not theaters, but missions within a geographic area. ISAF is not a theater, but a command.

OEF was the initial operation in the War on Terror and generally means the operations in Afghanistan and surrounding countries but is actually larger than that. It ended in DEC 14. OIF is what took place in Iraq from the invasion until DEC 11. ISAF is the International Security and Assistance Force, the NATO led mission in Afghanistan. US troops that were in Afghanistan thru DEC 14 were part of OIF and under the command and control of ISAF. ISAF has no role in Iraq or OIF.