(Bloomberg) -- Hess Corp. signaled its $53 billion agreement to be bought by Chevron Corp. may be delayed after Exxon Mobil Corp. filed for arbitration over the deal to preserve its rights to a massive oil discovery off Guyana.

Hess told employees in an email it was confident its arguments would prevail in the arbitration case Exxon filed with the International Chamber of Commerce. The company plans to offer more details about the timeline in its next merger update, according to the email made public Thursday in a regulatory filing. 

The disclosure marks the first time either Hess or Chevron have said Exxon’s push to safeguard its preemption rights in Guyana could delay their merger, initially expected to close by the second half of this year. It’s also the first time either company has been so explicit about their disagreement over how Exxon is interpreting its joint agreement with Hess and Chinese oil giant Cnooc Ltd. to produce oil off the coast of the South American nation.

“We disagree with ExxonMobil’s interpretation of the agreement and are confident that our position will prevail in arbitration,” Hess said in the email. “There is no possible scenario in which Exxon or CNOOC could acquire Hess’ interest in Guyana as a result of the Chevron-Hess transaction.” 

Hess shares rose as much as 1.7% Thursday. Chevron stock was up as much as 1.6%.

Read More: Exxon Deals Blow to Chevron-Hess Deal With Arbitration Case

Arbitration of this nature typically takes “five to six months,” Exxon’s senior vice president Neil Chapman said at a Morgan Stanley conference on Wednesday.

The discovery off Guyana is the world’s fastest-growing major crude development and stands at the heart of Chevron’s push to buy Hess. If Exxon succeeds in blocking the takeover, Hess would be required to pay Chevron a $1.7 billion break-up fee.

“We remain fully committed to the transaction and look forward to closing,” Hess said. 

In the meantime, Hess said it will continue to work with the US Federal Trade Commission as it reviews Chevron’s proposed takeover.

(Updates share prices in the fifth paragraph. A previous version corrected spelling of name in headline.)

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