In a saucepan of boiling water, blanch onions for 3 minutes then drain. Cool onions and peel.
In a large heavy skillet, heat oil over moderately high heat until hot but not smoking.
Sauté onions until lightly browned, about 5 minutes.
Add vinegar and water; simmer, stirring occasionally, until onions are tender, about 15 minutes.
Transfer onions with a slotted spoon to a platter, reserving liquid. Glazed onions may be prepared up to this point 2 days ahead with onions and reserved liquid chilled separately and covered.
Reheat onions in reserved liquid, adding a little water if necessary, and transfer with slotted spoon to platter.
Simmer reserved liquid until thickened, syrupy and reduced to about 1/2 cup.
Spoon sauce over onions and serve warm at room temperature.