* Big loss is worst showing in nearly 3 yrs; saw profit in Q2
* Indebted Pemex hit by dollar financing on peso slide
* Taxes gobble up over half of Pemex's income
By Mica Rosenberg
MEXICO CITY, Oct 27 (Reuters) - Mexico's state oil company Pemex on Thursday blamed exchange rate losses and taxes for a third-quarter loss of 81 billion Mexican pesos, its worst quarterly performance in nearly three years.
Pemex has not posted such a steep loss since the last quarter of 2008 when it suffered a loss of 115 billion pesos.
The company, which turned a profit during the first two quarters of this year, attributed the loss to the company's heavy tax burden and the peso's decline against the U.S. dollar.
"The net loss ... was the result of exchange rate losses of 49.2 billion pesos ($3.5 billion), derived from the depreciation of the peso against the dollar and the payment of taxes that represent 55 percent of total income," the company said in a statement to the Mexican stock exchange.
Pemex posted revenues of 392 billion pesos in the July-September period this year, up 23.5 percent from 317 billion in the third quarter of 2010.
Mexico's government relies on Pemex to fund about a third of the budget, forcing the company to borrow to pay for its capital investment programs. Pemex has struggled to increase oil output after a dramatic decline at its largest oil fields.
The company said its tax bill rose 35 percent in the quarter to reach 214 billion pesos.
Also, the Mexican peso lost more than 15 percent of its value in the third quarter due to global economic worries.
Mexico-based energy analyst David Shields said the big loss may have been linked to Pemex's debt payments.
Pemex's struggles have prompted calls for reform of the oil giant, and in August this year Mexico awarded its first private contracts for operating three small mature fields.
The current frontrunner for Mexico's presidential election in 2012, Enrique Pena Nieto, has also called for a shake-up of the company that has long been deemed a sacred cow since the country nationalized the oil industry in the 1930s.
In a controversial move, Pemex increased its stake in Spanish energy firm Repsol in August, forming a voting alliance with the largest shareholder, builder Sacyr .
The deal was opposed by Repsol and questioned in Mexico, since Pemex's own board was not consulted ahead of time.
But Pemex said it has the Spanish company's long-term interests in mind and hopes to access new technology for oil exploration in Mexico.
Pemex spent 1.2 billion euros to double its holding in the company to 9.492 percent, financing 70 percent of the transaction with debt. The share buy did not affect Pemex's investment budget, the company said.
A breakdown of the company's latest results showed that a 45 percent increase in Mexican Maya crude price in the third quarter compared to last year helped boost revenues. Mexico is a major oil exporter to the United States.
High oil prices pushed up revenues even as exports fell 4.1 percent to an average of 1.3 million barrels per day.
The company's performance during the third quarter compares with a loss of 2.8 billion pesos in the same period last year.
Pemex said it was able to maintain oil production in the quarter above 2.5 million barrels per day.
Preliminary data published by the national hydrocarbons commission on Thursday showed Pemex producing 2.562 million bpd in October, a jump from September's output.