"There is no sex tape," she says in a statement to PEOPLE on Tuesday. "There never has been one and there never will be one."
Until now, Bullock, 45, had not commented, remaining in seclusion since reports surfaced that James, 40, allegedly had cheated on her with at least four other women.
Bullock has been in touch with a close circle of friends, including comedian George Lopez, who visited her for a second time on Monday.
She spoke out in response to an online report that James possesses a graphic sex tape which he could possibly use as leverage in a divorce case.