LONDON, Sept 9 (Reuters) - Exxon Mobil ( XOM ) has

pulled out of the race to buy half of Galp Energia's

stake in a large oil discovery in Namibia that has attracted

interest from top energy companies, sources with knowledge of

the matter said.

More than 12 oil companies including Exxon, Shell

and Brazil's national oil company Petrobras had

expressed interest in Galp's 40% stake in the offshore Mopane

discovery, sources had previously said.

Galp is also proposing the buyer operate the field.

The reasons for Exxon's withdrawal from the process were

unclear. Other companies have continued to engage with Galp on

the sale, the sources said.

Exxon and Galp declined to comment.

Mopane is estimated to hold at least 10 billion barrels of

oil and gas equivalent and could be valued at more than $10

billion, according to some estimates.

The sale process follows a string of promising offshore

discoveries by Shell and TotalEnergies in recent

years, which raised the prospect of the south African country

becoming a major oil producing nation.

(Additional reporting by Sergio Goncalves; Editing by Jan

Harvey)