JOHANNESBURG, Oct 10 (Reuters) - South African national oil company PetroSA said on Thursday it planned to increase its debt as part of a capital expansion programme to revive its fortunes.

PetroSA, which operates the third largest gas-to-liquids refinery in the world, said net profit for the 12 months to the end of March fell 50 percent to 593 million rand ($59.34 million) from 1.2 billion the year before.

"An aggressive capital expansion program, which includes the Project Ikhwezi offshore development project and the envisaged acquisition of a downstream operation, will significantly change this scenario," said Webster Fanadzo, PetroSA's acting chief financial officer.

Project Ikhwezi is a $1 billion development off South Africa's south coast and is scheduled to come into production in the second quarter of 2014, with the gas providing supplies to PetroSA's Mossel Bay gas-to-liquids refinery, its primary revenue earner.

Mossel Bay has been operating at half of its capacity of 42,000 barrels per day due to a shortage of gas as offshore fields run dry. ID:nL6N0FO1MR

Ikhwezi is seen lasting till 2018 when liquid natural gas will be imported to Mossel Bay to sustain the refinery to 2020.

PetroSA was planning to spend between $375 million and $510 million building the infrastructure needed to import the gas. ($1 = 9.9925 South African rand)

(Reporting by Sherilee Lakmidas; Editing by Ed Stoddard)

((sherilee.lakmidas@thomsonreuters.com)(+27 11 775 3158)(Reuters Messaging: sherilee.lakmidas.thomsonreuters.com@reuters.net))

Keywords: SAFRICA PETROSA/