Growth in the country's eight infrastructure sectors rose to a 6-month high of 4.4 per cent in May this year, mainly due to a surge in output of coal and refinery products. These core sectors had grown 3.8 per cent in May last year. Coal output rose 7.8 per cent, refinery products output increased 7.9 per cent, and electricity generation rose 5.5 per cent in May this year. Crude oil production increased 0.8 per cent, and steel and cement grew 2.6 per cent, each, during the month. Fertiliser output increased 1.3 per cent. But natural gas recorded negative growth of 3.1 per cent in May.