(Adds details on drop in crude export sales and volumes, and production)
MEXICO CITY, April 30 (Reuters) - Losses at Mexican state-run oil company Pemex widened substantially in the first quarter, hit by a decline in export prices and volumes, it said on Wednesday.
The loss grew to 35.9 billion pesos ($2.75 billion) for the quarter from 4.33 billion pesos a year earlier.
Pemex's crude oil export sales fell by $6.8 billion due to a slide in the price of Mexico's exports, the company said in its filing with the Mexican stock exchange.
Crude export volumes were also down, by 1.1 percent, at an average of 1.19 million barrels per day for the quarter.
Mexico's government relies on oil revenues to fund about a third of the federal budget.
For the quarter, Pemex said its tax bill was 210 billion pesos ($16.09 billion).
Revenue rose nearly 3 percent to 407 billion pesos.
Mexico is the world's No. 10 crude producer and the third-largest exporter to the United States, but it must import nearly half of its gasoline due to a lack of domestic refining capacity.
The company said average crude production had reached 2.492 million bpd for the quarter, down 2.1 percent from a year earlier.
Since hitting peak production of 3.38 million bpd in 2004, Mexican crude output has slid by a quarter to settle at 2.52 million bpd last year. Crude exports have dropped by a third over the same period.
In December, Mexico's Congress passed landmark energy reform legislation that ended Pemex's 75-year monopoly on oil production and aims to lure significant new streams of private investment via new contracts to boost output.
Pemex's crude output in March averaged 2.47 million bpd, the lowest since 1995.
($1 = 13.06 pesos at end of March) (Reporting by Dave Graham and David Alire Garcia; Editing by Lisa Von Ahn)