1996-1997 Cadillac DeVille, Eldorado and SeVille and 1997-1999 Cadillac Catera all used the same pair of seat memory keyless entry remotes. The GM part number for Fob #1 is 16259819, which is RUI part 138-1138. The GM part number for Fob #2 is 16259829, which is RUI part 139-1139. These are both 4-button keyfobs with lock, unlock, trunk and (locking) gas cap release button icons. They have FCC ID ABO1602T on the back of the case, along with the fob number and some other information.
If you are buying one of these remotes, please note the programming situation. The keyless entry systems in 1996-1997 Cadillac DeVille, Eldorado and SeVille vehicles are all user programmable. However, if you own a 1997-1999 Catera, programming your system to accept a replacement remote requires a scan tool, which means you will probably have to take your vehicle and all remotes used with it to a dealership for programming.