* Company logs first sale of 800,000 barrels in Oct
* OGX posts first revenues from oil sale of 150 mln reais
* Gas treatment plant to start up in early 2013
SAO PAULO, Nov 8 (Reuters) - OGX Petroleo e Gas SA , Brazil's second-largest oil company by market value, reported on Thursday a net loss of 343.6 million reais ($168 million), after logging its first accountable revenues from crude oil sales.
In the second quarter, OGX recorded a loss of 398.7 million reais ($196.7 million), due to a mix of currency-related, financial and drilling costs.
After OGX's first wells came on line in January and February, the company said it logged its first sale of roughly 800,000 barrels of oil to Reliance Industries Ltd in October.
Earnings before interest, taxes, depreciation and amortization, a gauge of operating profit known as EBITDA, improved to a negative 51.6 million reais compared with a negative 110 million reais for the April-June period.
OGX is controlled by Brazilian billionaire Eike Batista and is the flagship company of his EBX energy, transportation, mining, shipbuilding and real estate group.
The company produced an average 9,300 barrels of oil equivalent per day in the third quarter from its Tubarao Azul field, up slightly from the 9,100 barrels a day in the second quarter. The field produced 856,800 barrels since startup.
OGX shares closed little changed on Thursday before the results were released, at 4.77 reais in Sao Paulo trading. Since January, shares have fallen 73 percent.
OGX said it expects to begin producing from three wells in its Tubarao Martelo field in the Campos basin in late 2013, after the arrival of its floating production, storage and offloading (FPSO) vessel OSX-3.
A third completed well is about to be connected in the coming weeks to FPSO OSX-1, which is now producing in the Tubarao Azul field.
All of the production wells in the Gaviao Real project in the Parnaiba basin are ready and are being connected to the natural gas treatment plant, which is expected to begin startup operations in early 2013, the company said.
The company has received environmental clearance for drilling in the BM-C-37 and BM-C-38 fields in the Campos basin and has made what it calls important hydrocarbon discoveries in the Parnaiba basin at the Bom Jesus deposit.
The company said it also got clearance from the national oil agency ANP to drill in ultra-deep waters.
OGX expects to reduce its capital expenditures budget to $1.2 billion in 2013, as it slows its drilling campaign in the Santos and Campos basins, pares back its drilling rig fleet and shifts its focus to production from exploration.
$1 = 2.04 Brazilian reais Reporting by Reese Ewing and Jeb Blount; Editing by Bernard Orr