Warm a large heavy pot over medium heat and add the oil.
Drop in 2–3 kernels, cover, and wait until they pop.
Add the remaining kernels and sprinkle in the sugar; stir quickly to coat.
Cover, reduce heat slightly, and shake the pot often, venting the lid a crack to release steam.
Keep cooking and shaking until popping slows to 2–3 seconds between pops, then remove from heat.
Immediately spread popcorn on a large sheet pan, sprinkle with salt, and toss. Cool briefly, then break up any clumps.