After months of experimenting with long-form video, YouTube said on Friday it would start offering full-length episodes of some television shows on its sprawling Web site.

The staggering growth of YouTube  five billion videos were viewed there in July  has come primarily from short videos that last only a few minutes. But Internet users are gradually becoming more comfortable watching longer videos online, prompting YouTube’s commitment to the format.

“This is what the users want,” said Jordan Hoffner, the director of content partnerships for YouTube.

With the addition of TV series like “Dexter,” “Beverly Hills, 90210” and “Star Trek” through a deal with CBS, YouTube is catching up to other Web sites that have promoted long-form video for some time.