The Bord Gáis Energy index decreased by 3% in September despite rises in the price of gas, electricity and coal in the month.

The index, which tracks wholesale commodity prices, fell for the first time since June on the back of a 7% fall in oil prices due to easing geopolitical tensions. The index stood at 143 in September.

''The fall in Brent crude oil prices was the key factor driving the 3% drop in the index month-on-month which superseded rising wholesale gas, coal and electricity prices," commented Bord Gais power trader John Heffernan.

He said that the ongoing rise in wholesale UK Day-ahead gas prices was of particular note.

"The prolonged gas demand in the winter of 2012/2013 influenced prices throughout the summer months as market participants replenished depleted stock levels amid heavy summer maintenance and reduced supplies. This resulted in record summer trading levels for wholesale gas which will influence prices in the months ahead," he added.

Bord Gáis said that the price of Brent crude oil fell by 7% in euro terms as tensions in Syria and Iran eased after months of uncertainty. It noted that the restarting of Libya's oil industry after strikes and protest was especially relevant and supply constraints decreased over the month.

But natural gas prices were 4% higher in September. Bord Gáis said that, unusually, wholesale gas prices over the summer months were in line with levels seen in December and January due to the unprecedented demand for gas storage injections after the complete depletion of stocks by the end of March. This coincided with very low Qatari LNG deliveries to the UK.

The Rotterdam monthly coal futures contract rose by 7% in September due to higher freight costs and increased trader anxiety by the loss of a substantial amount of the fuel due to the 53 day strike in Colombia.

In September, the monthly average Irish wholesale electricity price rose 5% month on month with pressure from the combination of rising wholesale gas prices and carbon prices.