Place the Oreo cookies in the refrigerator to chill. Next, line a plate with paper towels. Set aside.
In a large pot, heat the oil over medium-high heat until it has reached a temperature of 375 degrees on a digital instant-read thermometer.
Meanwhile, in a medium bowl, whisk together the pancake mix and water until smooth.
Remove the Oreo cookies from the refrigerator. Using a pair of tongs, dip each Oreo cookie into the pancake batter, coating the entire surface. Carefully lower each coated cookie into the frying oil. Only fry 3-4 cookies at a time to not overcrowd the pot.
Fry each cookie until golden-brown, about 1-2 minutes. Flip, then brown the other side. Remove the cookie with a slotted spoon to the paper-towel-lined plate before serving. Serve immediately with a dusting of powdered sugar.
Deep-fried Oreo cookies are best enjoyed fresh, immediately after they are fried. Although they may be consumed the following day, they will be soggy and have an oily texture.