How Late I can apply for my H1B petition extension?

[Senkmar]

Friends,

How Late I can apply for my H1B petition extension, my current Petition/Visa/I-94 expires on Sept 30 2013?

Since my passport is expiring next year April, I Applied for passport renewal, but I am yet to receive my passport back. Also since my current project is completing by Jun 30. I need to look for a new project and apply for extension (same employeer). Any information will be much helpful. ]

Thanks in Advance.

Thanks
Senthil