Gas prices in Northern Ireland fell during May thanks to imports of liquified natural gas and other factors, according to the firmus energy index.
Weakening demand brought by rising temperatures also contributed to a 7% drop in gas prices, the energy provider said.
The cost of oil eased by just 1% after showing a climb of around $12 during April.
Firmus suggested that May's performance showed that the recovery in prices from January's low of $47 a barrel had now ground to a halt.
And the company said that the future "looks a little uncertain" thanks to geopolitical factors and their impact on the price of gas.
Firmus Energy director Des Brown said: "Russian gas, the cost of which is linked to the lagged price of oil, should continue to get cheaper. But the Ukrainian/Russian conflict might mean an interruption to those lower cost supplies."
The falling price of gas also led to lower electricity costs, with the wholesale cost of power dropping by 9% month on month. But windy weather played a part too, as active turbines displaced more expensive power stations from the grid, firmus said.