Most electric deep-fryers use between 6 and 19 cups of oil; our winner uses slightly under 15 cups. This is more than enough oil for most of our recipes; when deep-frying in a Dutch oven, we typically use 8 to 12 cups. You can use either peanut or vegetable oil; we have no distinct preference in the test kitchen. Don't be tempted to put more oil in! You don't need it, and if there's too much oil, the bin can overflow when you put food in.
The greatest advantage of an electric deep-fryer is that once you set its temperature, the appliance will automatically regulate the temperature for you—no need to fuss with the controls or use an additional thermometer to check on it. All the fryers we tested were reasonably accurate within the temperature ranges we chose, too.
Electric deep-fryers heat up oil fairly quickly—our winner takes 14 to 15 minutes, depending on the temperature chosen, compared to about 20 minutes for the same amount of oil in a Dutch oven. You'll know when our winner is at the right temperature because the indicator light on the console will switch off. We recommend adding delicate food (such as doughnuts) or battered/breaded foods (such as fried chicken) in a single layer to the basket to encourage even cooking and prevent individual pieces from sticking together.
Most electric deep-fryers can be covered in order to contain spatters while the food inside is cooking—a benefit that helps keep your counters clean. The fryers do such a great job of regulating the temperature that as long as you haven't exceeded the volume of oil recommended and don't overcrowd the fryer, the oil and food should sit low enough in the fryer that there is no risk of the unit overflowing, as there might be if you covered a Dutch oven.
We love the baskets that came with most of the electric deep-fryers we tested. They allow you to remove all the food in the fryer at once, and can be latched onto a hook on the side of the fryer to allow excess oil to drain.