In a large pot, heat oil over high heat. Add the unpopped popcorn. Moving the pan constantly, pop the corn. Remove from heat, place in a large baking pan, and keep warm in the preheated oven. Discard unpopped kernels.
Mix sugar, butter, corn syrup, and salt into a large saucepan. Cook over medium heat, stirring until mixture starts to boil. Continue cooking for 5 minutes without stirring.
Remove from heat. Stir in baking soda and vanilla. Pour over the popped popcorn. Stir popcorn until evenly coated. Bake for 25 to 30 minutes in the preheated oven, stirring every 10 minutes. Remove from pan and put into a large bowl to cool.
