WASHINGTON, Sept. 11 — A group of oil companies led by Chevron, which said last week that they had discovered a huge new oil field in the Gulf of Mexico, could avoid more than $1 billion in royalty payments to the federal government for the oil.

The potential bonus to Chevron and its partners stems from a mistake the Interior Department made in signing offshore leases in the late 1990’s for drilling in federal waters. The magnitude of the oil discovery — estimated in a range of 3 billion to 15 billion barrels — is likely to intensify a battle in Congress over incentives for drilling in publicly owned waters.

Under pressure from lawmakers, Chevron and other big producers have said that they would renegotiate their leases. But they have not said how much they are willing to give up, and the Interior Department has virtually no bargaining power under current law.

Chevron and its partners, Devon Energy and Statoil ASA of Norway, have six leases in the Jack oil field, about 175 miles off the coast of Louisiana. Two of the leases allow the companies to avoid royalties on as much as 87.5 million barrels of oil per lease.