Energy industry sources have told RTÉ that Irish electricity and gas users will see little benefit from the 31% fall in oil prices this winter.
Long-term contracts entered into by energy companies and problems with gas supplies mean prices will remain high.
The ESB increased prices by 17.5% on 1 August and gas costs rose by 20% at the beginning of the month.
In July oil prices reached a record of $147 a barrel.
Since then, fears of a global economic slowdown have resulted in sharp falls.
Gas and oil prices tend to move in tandem but pipeline problems have kept gas prices high this winter.
ESB and Bord Gáis booked most fuel requirements at fixed prices for the peak winter period in the summer.
In addition, increased prices will be reviewed in November with a price rises expected in January.
Meanwhile, the cartel of major oil producing countries, OPEC, will cut its output in response to falling prices. A barrel of crude oil has fallen below $100 for the first time since April.
OPEC President Chakib Khelil said he did not believe the cut would stop prices falling.
