* Exxon, Petronas and Ophir among the firms chosen
* Gabon hopes to reverse chronic oil decline
DAKAR, July 21 (Reuters) - Gabon's oil ministry said on Monday it has selected seven firms for a final round of negotiations as part of an offshore licensing round the government hopes will reverse a chronic decline in output.
The new blocks are located in deep offshore waters - an exploration play that is expensive and uncertain but potentially very rewarding given the similarity of geological structures to oil-rich Brazil, where billions of barrels of oil have been discovered.
Former OPEC member Gabon produces around 230,000 barrels per day (bpd), down from a peak of close to 400,000 bpd in the 1990s.
An oil ministry statement said Impact Oil & Gas, Repsol , Perenco, ExxonMobil, Marathon, Petronas and Ophir were ranked highest after bidding for a total of nine blocks.
"These companies listed are invited to finalise negotiations for the signature of the relevant CEPPs (exploration and production sharing contracts) as soon as possible," according to a statement signed by Minister for Oil and Hydrocarbons Etienne Dieudonne Ngoubou.
The statement showed that other companies such as Cobalt , Noble, Royal Dutch Shell and Total had been ranked in second or third place for the blocks.
The ministry said it had the right to open negotiations with the lower-ranking firms if talks with the first-choice companies were unsuccessful.
Bids for another eight blocks offered during the licensing round "did not reach the expectations of the Gabonese Republic", the statement added. (Reporting by Emma Farge; editing by Keiron Henderson)