By Rakesh Sharma 
 

NEW DELHI--India's crude-oil production rose by a marginal 0.5% in May, while natural gas output continued its declining trend for the 18th straight month, underlining the South Asian nation's struggle in maintaining production at its ageing assets.

Crude-oil output in May rose to 3.25 million metric tons, equivalent to 768,200 barrels a day, from 3.23 million tons, or 764,700 barrels a day, in the year-earlier period, the oil ministry's provisional data showed. Oil production missed the government's estimate of 3.33 million tons.

India, which meets more than three-fourths of its crude-oil needs through imports, has been trying to increase domestic production. But the poor prospectivity of its sedimentary basins and ageing and depleting fields has kept its ambitions under tight check.

Oil & Natural Gas Corp. (500312.BY), India's flagship oil explorer, saw its May crude-oil output decline 4.1% on year to 1.91 million tons, or 452,300 barrels a day, the data showed.

ONGC's crude-oil production has been declining for several years as its major producing field, Mumbai High, has been in production for several decades and the company hasn't been able to bring any new major fields into production.

Natural gas output in India declined 10.8% in May to 3.70 billion cubic meters from 4.14 billion cubic meters in the year-earlier period. However, it exceeded the government's estimate of 3.45 billion cubic meters.

The decline in natural gas output was mainly due to a fall in output at Reliance Industries Ltd.'s (500325.BY) east coast block.

Reliance produced 42 million standard cubic meters a day of gas from the D6 block in the Krishna-Godavari Basin in the fiscal year ended March 31, well below its original target of 70 mmscm/d. Output is estimated to decline to 20 mmscm/d by March 2015.

Reliance is working with its partner BP PLC (BP), which owns a 30% stake in the block, to understand the complex geology of the block and hopes to add around 30 mmscm/d production by developing some new fields in the block, Chairman Mukesh Ambani said June 7.

Write to Rakesh Sharma at rakesh.sharma@dowjones.com