Red Hat Enterprise Linux 3

General Availability               23.10.2003.
End of Production Phase 1   20.07.2006.
End of Production Phase 2   30.06.2007.
End of Production Phase 3   31.10.2010.
End of Extended Life Cycle  31.10.2013.

Red Hat Enterprise Linux 4

General Availability              14.02.2005.
End of Production Phase 1   31.03.2009.
End of Production Phase 2   Q1 2011
End of Production Phase 3   29.02.2012.
End of Extended Life Cycle  28.02.2015.

Red Hat Enterprise Linux 5

General Availability              15.03.2007.
End of Production Phase 1   Q4 2011
End of Production Phase 2   Q4 2012
End of Production Phase 3   31.03.2014.
End of Extended Life Cycle  31.03.2017.

Red Hat Enterprise Linux 6

General Availability              10.11.2010.
End of Production Phase 1   Q4 2014
End of Production Phase 2   Q4 2015
End of Production Phase 3   30.11.2017.
End of Extended Life Cycle  30.11.2020.

• Production 1 Phase

During the Production 1 phase, at a minimum, qualified security Errata Advisories of important, critical impact and urgent priority bug-fix errata may be released as they become available.
If available, new or improved hardware support and select enhanced software functionality may be provided at the discretion of Red Hat, generally via Service Packs. Hardware support that does not require substantial software changes may be provided independent from Service Packs at the discretion of Red Hat.
Service Packs will also include available and qualified Errata Advisories. Service Packs are cumulative thus including the contents of previously released updates. The focus for Service Packs during this phase lies on resolving defects of medium or higher priority.
Updated install images will be provided for Service Packs during the Production 1 phase.

• Production 2 Phase

During the Production 2 phase, at a minimum, qualified security Errata Advisories of important, critical or urgent priority bug-fix errata may be released as they become available.
If available, refreshed hardware support that does not require substantial software changes may be provided at the discretion of Red Hat, generally via Service Packs. New software functionality is not available during this phase.
Service Packs will also include all available and qualified errata. Service Packs are cumulative thus including the contents of previously released updates, including those from Production 1 phase. The focus for Service Packs during this phase lies on resolving defects with a minimum priority of high.
Updated install images will only be provided for Service Packs during the Production 2 phase if required due to installer changes at Red Hat's discretion.

• Production 3 Phase

During the Production 3 phase, at a minimum, qualified security Errata Advisories of critical impact, as well as, selected urgent priority bug-fix errata may be released as they become available.
No new functionality, new hardware support or updated installation images are planned for release in Production 3 phase. There are no Service Packs planned during this phase.

• Extended Life Cycle Phase

During the Extended Life Cycle Phase, active subscribers continue to receive access to previously released content on RHN as well as other content such as documentation and the Red Hat Knowledge Base through the Red Hat customer portal.
As an optional add-on to a regular Red Hat Enterprise Linux subscription, Red Hat offers Extended Life Cycle Support (ELS) Subscriptions.
ELS provides critical impact security fixes and selected urgent priority defect fixes that are available and qualified for a subset of the packages in a specific major releases of Red Hat Enterprise Linux beyond the end of its regular 7-year life cycle. For ELS subscribers, Red Hat will generally continue to provide the critical impact security fixes independent of customer requests.
The individual ELS streams will be maintained for an additional 3 years after the end-date of the Regular Life Cycle of the relevant release (extending the Life Cycle to 10 years). ELS is provided for a limited set of software packages on a limited number of hardware architectures.

Source: www.redhat.com