MEXICO CITY, April 14 (Reuters) - Mexico's proven oil and gas reserves fell 3.1 percent in 2013, according to energy ministry data, as the nation's once-ample shallow water deposits begin to run dry.
The proven Mexican reserves totaled 13.439 billion barrels of oil equivalent (boe), or down by nearly 430 million boe compared with the previous year.
Nearly three-quarters of the reserves, or 9.812 billion boe, are made up of crude oil.
The new estimate for so-called 1P certified reserves was set on Jan. 1, 2014, and covers oil and gas fields believed to have a 90 percent chance of being extracted with existing technology.
Mexico, the world's tenth-biggest crude producer, has not been able to discover and certify new oil and gas fields as fast as it has extracted resources from current production.
Proven oil and gas reserves reached 13.868 billion boe as of Jan. 1, 2013.
Reserves have remained relatively stable since 2009, but Pemex's lack of investment in exploration over many years has led to a precipitous decline in the country's reserve base.
Mexico boasted proven reserves of about 55 billion boe in 1990, but reserves have fallen sharply since.
Mexico has the third-largest proven oil reserves in Latin America, behind Venezuela and Brazil.
A landmark energy reform passed in December promises to lure major new streams of private investment into Mexico's oil and gas sector, eventually boosting reserves and output.
Secondary legislation that will set commercial and other regulatory terms of the reform championed by President Enrique Pena Nieto is expected by May. (Reporting by David Alire Garcia; Editing by Meredith Mazzilli)