HOUSTON, March 19 (Reuters) - Chevron ( CVX ) was surprised when

Exxon Mobil filed for arbitration over Chevron's ( CVX ) plans to buy

Hess's Guyana oilfield stake, Chevron ( CVX ) CEO Michael Wirth said on

Tuesday.

Chevron ( CVX ) announced plans to buy Hess last year, and the

Guyana stake is Hess's most valuable asset.

Chevron ( CVX ) had done extensive due diligence on the operating

agreement between Exxon and Hess in Guyana and has extensive

experience in those types of agreement around the world, Wirth

said.

Chevron ( CVX ) had been in talks with Exxon over the matter, he

said. Exxon, which operates the Guyana oilfield, says it has the

right of first refusal for Hess's stake.

"We were surprised when they a couple of weeks ago abruptly

ended those discussions and publicly announced... they had filed

for arbitration."