US TV
The medical drama, in its 15th year, will now run for 21 episodes, according to The Hollywood Reporter.
As part of the agreement, ER producer John Wells's cop show Police has been granted a six-episode order by NBC.
Wells had initially turned down a 12-episode request for Police because he feared the show, which was being primed for the 10pm slot, would be sidelined when Jay Leno's new talkshow debuts at that time in September.
The longer ER season may result in new drama Kings being moved to another night, as it was intended to bow on March 12 after ER's finale.
More: John Wells, US TV
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