(Adds details of earnings, merger context, analyst comment)
SAO PAULO, Aug 6 (Reuters) - Grupo Oi SA, Brazil's biggest fixed-line telecommunications operator, posted a second-quarter net loss on Wednesday, as revenue stagnated and payroll and debt-servicing costs rose amid a troubled merger with its largest shareholder.
The company posted a quarterly loss of 221 million reais ($97 million), its first results since combining assets with Portugal Telecom SGPS SA in April. The result was larger than the combined shortfall of 124 million reais the companies would have posted together a year ago, according to a securities filing.
Revenue in Brazil slipped 2 percent from a year earlier to 6.94 billion reais. Revenue from Portugal fell 3.4 percent in euros, but a currency swing boosted results in Brazilian reais by nearly 10 percent. As a result total revenue was little changed at 9.02 billion reais.
Earnings before interest, taxes, depreciation and amortization, a gauge of operating profit known as EBITDA, fell 21.3 percent to 2.55 billion reais.
According to André Baggio, an analyst with JPMorgan Securities, EBITDA was hurt by interconnection costs following a 25 percent rate cut in mid-February, higher marketing and television content expenses and a spike in leasing expenses due to tower sales over the past year.
The second quarter "was another weak quarter with (profit) margin deterioration," Baggio said in a client note.
Earnings did not take into account a debt investment of 897 million euros ($1.2 billion) that Portugal Telecom made in Luxembourg-based investment vehicle Rioforte without disclosing it to Oi. Rioforte defaulted last month and Portugal Telecom agreed to bear any losses, accepting a smaller share of their combined company.
Still the merger, aimed at bolstering Oi's balance sheet, has left it with more in debt, with gross debt rising to 52.2 billion reais in June from 34.5 billion reais in March. Subtracting cash, net debt rose 52 percent to 46.2 billion reais.
Due to questions about how results would be announced and potential conflicts of interest from banks involved in the merger, few analysts had provided comparable earnings forecasts. ($1 = 2.29 Brazilian reais) ($1 = 0.7495 euros) (Reporting by Brad Haynes and Guillermo Parra-Bernal; Editing by Jeffrey Benkoe)