Oksana Grigorieva denied under oath that she's the source of the leaked Mel Gibson tape, TMZ has learned.


Mel's lawyer, Stephen Kolodny, took Oksana's deposition Friday.  Although it was secret, TMZ has learned Oksana was asked squarely if she leaked the tape -- which she was prohibited from doing by the judge in the custody case.

We're told she emphatically denied being the source of the leak.