Although a full 22 episodes were ordered, only 12 episodes were filmed and completed before the strike. This includes the special 100th episode. The strike is officially over. And some other good news comes with it. The CW has requested to shoot 5-6 more episodes that will air in April/May.

Executive Producer Mark Schwahn wrote:
Although we have six new episodes left, no one is more excited about the end of the strike than we are at One Tree Hill. With our four-year jump ahead, we're having an outstanding year creatively, and despite standing alone on Tuesdays, our numbers are routinely second only to Smallville for scripted dramas at the CW. We'd love the opportunity to continue season five, and if the WGA's new contract is ratified, hopefully we'll be able to do just that. If not, we'll see you for season six.

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Edit:
One Tree Hill will be back on Monday, April 14 with six new episodes beyond the 12 that have already been produced. The last pre-strike episode should air on March 18, leaving viewers hanging for about a month. There's no word on whether the CW is moving One Tree Hill to Mondays permanently, but it's possible they may want to pair it with Gossip Girl to prepare for the return of Reaper on Tuesdays.