Mexico's state-owned oil company Pemex posted its 10th consecutive quarterly loss in the first quarter, as it was hit hard by lower crude prices and higher financial expenses, the firm said on Thursday.

Pemex's 100.5 billion peso (US$6.6 billion) quarterly loss was nearly three times as large as the company's loss in the same period last year.

Revenue for the January through March period fell sharply to 279.5 billion pesos, compared with revenue of 407 billion pesos in the year-earlier period, the company said in a filing with the Mexican stock exchange.

The average price of Pemex's crude oil export mix during the quarter was US$45 per barrel, down by more than half from US$92 during the same quarter last year.

"We expect that this oil price slump is not permanent. This is a cyclical industry in which the oil price behavior is sometimes up and sometimes down," said Gustavo Hernández, head of the company's exploration and production unit, in a call with analysts.

Crude export volumes, however, were up about 6 percent on the quarter to 1.263 million bpd, compared to shipments of 1.19 million bpd in the year-earlier period.

The company said average crude oil output was 2.3 million barrels per day for the quarter, down 7.7 percent from a year earlier when Pemex produced an average of 2.492 million bpd.

Hernández said heavy crude oil production was down by over 12 percent during the quarter, while extra light crude output fell by more than 13 percent.

He noted Pemex expects 2015 crude output to average 2.3 million bpd, down from a previous forecast of 2.4 million bpd, despite a platform explosion earlier this month that killed four workers. Three others still remain missing.

Pemex's production has dipped by nearly a third since hitting a peak of 3.38 million bpd in 2004.

Last year, Mexico's Congress finalized a sweeping energy overhaul that ended Pemex's decades-long monopoly on oil production. The reform aims to lure billions of dollars in private investment via new contracts to boost output.

Mexico's so-called Round One tender, in which oil companies will for the first time be able to bid on contracts covering 169 offshore and onshore blocks, was launched late last year and the first awards are set for July.

The energy ministry said earlier this month it expects the tender's first two packages of shallow water contracts to generate investment of US$21.3 billion.