In a saucepan, combine water, sugar, salt, and vegetable oil. Bring to a boil over medium heat.
Remove from heat and stir in flour until the mixture forms a smooth dough.
Heat oil in a deep pan to 350°F (175°C).
Transfer dough to a pastry bag fitted with a star tip.
Pipe 2–3 inch pieces of dough directly into the hot oil. Fry in small batches for 2–3 minutes or until golden brown, turning halfway through.
Remove churros with a slotted spoon and drain on paper towels.
Combine cinnamon and sugar in a shallow bowl. Roll warm churros in cinnamon sugar until coated.
Serve with chocolate, caramel, or dulce de leche for dipping.