(Adds Pemex comment explaining outlook for natural gas production)

By Ana Isabel Martinez

MEXICO CITY, Aug 29 (Reuters) - Mexican state oil giant Pemex on Friday forecast its crude oil output would average 2.4 million barrels per day (bpd) in 2015, which could mark the first year that crude production at the company has risen in over a decade.

The company expects output of 2.35 million bpd this year.

Meanwhile, Pemex's natural gas production is seen falling next year by over 12 percent compared with the average output reported through the first seven months of this year.

A company spokesman said that the dip is explained by more accurate measuring techniques now being implemented and that natural gas output in 2015 would actually be "similar" to this year.

President Enrique Pena Nieto signed into law this month the final elements of a sweeping energy overhaul aimed at reversing declining crude production and luring billions of dollars in private investment to the sector.

The reform ended Pemex's 75-year monopoly, and it will now be able to enter into first-ever joint ventures with oil majors.

Gustavo Hernandez, head of Pemex's exploration and production arm, told reporters that next year's gains will come from a mix of better-producing mature fields as well as new fields. He pointed to the heavy oil Ayatsil-Tekel-Utsil field, located in the shallow waters of southern Gulf of Mexico, which he said will begin commercial production in October.

The Ayatsil-Tekel-Utsil field contains some 750 million barrels in proven and probable reserves, the most of any of the 10 fields for which Pemex has said it will seek partners.

Among the first steps of the energy reform, Pemex will seek joint ventures for a mix of both onshore and offshore fields it was assigned in the so-called Round Zero allocation. Those ventures are expected to generate investment of $32.3 billion.

Hernandez said 2015 natural gas output is estimated at 5.7 billion cubic feet per day (bcf/d). Natural gas production so far this year averages 6.5 bcf/d, according to Pemex data.

The company is, however, changing how it measures natural gas production, stripping out nitrogen and carbon dioxide which were previously counted in reported output.

Hernandez added that Mexico, the world's 10th biggest crude producer, should deliver some 2.8 million bpd by 2018, including output from Pemex and new entrants into the market.

Pemex last week lowered its crude oil output forecast for 2014 as it sought to measure its production more accurately.

Pemex has made several adjustments to its forecasts in recent weeks and over the years has frequently fallen short of the targets.

(Writing by David Alire Garcia; Editing by Leslie Adler)