Heat the oven to 500°F. In a large bowl, whisk together the oil and salt and pepper. Add the grapes and toss very gently to coat with mixture, being careful not to break the clusters too much.
Arrange in a single layer on a baking sheet. Roast until the grapes are lightly browned and the skins are slightly crisp, about 12 minutes.
(I roast then during the first half hour of my turkey, then take them out and let them stand until the turkey is finished. They are tasty at room temperature!)