LIBREVILLE, MARCH 13 (Reuters) -- Gabon, Africa's seventh largest oil producer, is offering 42 additional offshore deepwater and ultra-deepwater oil blocks for exploration, the government said on Friday.

The West African nation, which currently produces roughly 250,000 barrels of crude oil per day and relies on energy for about half of its gross domestic product, is seeking bids from international firms by May 5, it said.

The country will "engage in a marketing plan for the Gabonese oil sector in the financial centers of Paris, Houston, Singapore, London and the Canadian city of Calgary," a government spokesman said.

Gabon's oil sector, one of the continent's most mature and already home to several international oil companies including France's Total, has been in decline since the late 1990s when output was over 350,000 bpd.