As posted months ago, Exxon did make a final attempt to buy the operatorship of Block 4 with Anadarko when they sent a team to Nigeria, Sao Tome and the JDZ after awards had been announced.
They were turned down because awards had been announced and accepted.
IMHO Nigeria did give Exxon another deep ocean block which I believe they are already drilling.
Personaly, I agree with S. Freed that Addax is a better fit for the JDZ and ERHC in Block 1 than Exxon was.
Exxon was not cooperating with anyone, not even Chevron.