On the basis of an America's Test Kitchen recommendation, I purchased this heavy-gauge baking pan and, just as ATK said, it doesn't warp in the oven. No baking sheet, however sturdy, can survive being shipped across country in an unpadded plastic bag without some damage. Mine arrived scratched and a little dented. I wrote to complain to the seller, but have not received a response. This is a great baking pan, but exercise caution if purchasing it from Next Day Gourmet.

I received the 18 gauge model (model number 5303), and so far it has not warped after 15 minutes in a 500 degree oven...

Here is my own speculation on all of this warping vs. non-warping business: I think the warping vs. non-warping on the 13 gauge model (5314) is probably just variation in manufacturing and quality control issues on the part of Lincoln.

I do wonder whether the 18 gauge model, even though it's thinner than the 13 gauge model, is less likely to warp. From what I can gather, the 13 gauge has a "sanitary open bead", which make it easier to clean and sanitize, which is what make it NSF-rated. I'm guessing that because the 18 gauge model has a closed bead with a bead wire, that makes it less likely to warp. Here is a PDF made by Next Day Gourmet I found on the net that explains some of the differences between the various terms that apply to baking sheets, and when they are supposed to recommend one model over another: [..]

Like others who bought this item based upon the Cook's Illustrated recommendation, the pan warped at its first use! Other than that, it is sturdy and good, just permanently warped!

This is a heavy duty pan, but it did warp the first time I used it in an oven. I, too, followed the recommendation of Cook's Illustrated to buy this pan because "Pan can't be twisted, did not warp." Well, at a mere 425 degrees the pan did warp.

The pan I received warps at 400 degrees and above. On the back is stamped Wear Ever 5314. I contacted Lincoln directly and I was told that they do manufacture Wear Ever but it is obviously the inferior product. They are sending me their 5303 pan which has a concavity and bead wire per their description, and is non-warping because of this. The Amazon order was fulfilled by a third party retailer and I apologize that I do not have the name with me, except that it contained the word "Gourmet". I suspect America's Test Kitchen tested the 5303 pan. If you order by clicking this link you may have the same problem.