HOUSTON (Reuters) - Shares in U.S. oil producer Hess suffered their largest daily percentage drop in 20 months on Thursday on fallout from the lengthy new delay to its proposed sale to Chevron ( CVX ).

An arbitration panel organized to hear an Exxon Mobil ( XOM ) challenge to the $53 billion sale will not meet until next May, pushing back any closing until the second half of 2025. The two companies originally had hoped to conclude the merger earlier this year.

Hess' stock fell $11.25, or 7.35%, the largest daily percentage drop since November 2022. Chevron ( CVX ) shares were also off 4%, or $6.57, at $153.93 in midday New York trading on Thursday.

Exxon and CNOOC Ltd (0883.HK) filed arbitration claims claiming a pre-emption right to any sale of Hess' lucrative stake in a Guyana oil-producing joint venture. The challenge threatens to block Chevron's ( CVX ) biggest deal in more than two decades.