Combine chili powder, garlic salt and oregano in a small bowl; set aside.
Pour oil in a deep, heavy saucepan. Heat, covered, for several minutes over medium-high heat. Lift the lid and put in a kernal of popcorn. When it pops, the oil is hot enough to add the remaining popcorn. Replace the lid and pop the corn, shaking the pan to avoid scorching. Remove from heat when popping has stopped. Let sit about 30 seconds to ensure all kernels are popped. Remove lid.
Place popped popcorn in large plastic or paper bag; sprinkle with seasoning mixture. Close bag and shake to evenly distribute seasoning.
Drizzle butter over popcorn. Immediately close bag and shake until popcorn is evenly coated. Serve at once.