Release: Unocal receives waiver enabling it to engage in discussions with CNOOC

(El Segundo, Calif., June 23, 2005) - Unocal Corporation (NYSE: UCL) announced today that it has received a waiver from Chevron Corporation enabling Unocal to engage in discussions with CNOOC Limited and its representatives concerning a transaction proposed by CNOOC Limited at any time until the date of the Unocal stockholder vote on the proposed merger with Chevron.

The date of the Unocal stockholder meeting has not yet been set.

Unocal intends promptly to commence such discussions with CNOOC Limited. There can be no assurance that any agreement with CNOOC Limited will be reached. In connection with entering into the Chevron merger agreement, the Unocal board of directors recommended the transaction to Unocal stockholders. That recommendation remains in effect.(end of release)