Editor: Lauren, oven cleaner usually includes some heavy-duty chemicals, so I would play it safe and just replace the baking sheet. You might want to introduce your roommate to Bar Keepers Friend for handling tough stains next time — it really works!
Readers, what do you think? Is the baking sheet still safe to use? And what do you use to remove baked-on grease from baking sheets?
Related: In Praise of Battered Baking Sheets
(Image: Emma Christensen)