Centrica-owned British Gas said it will reduce gas prices by 5.1%, benefiting ar ound 6.8 million customers, while rival EDF Energy is to bring down its standard gas tariff by 5%, making bills cheaper for around 900,000 customers.
The reductions follow announcements by rivals npower, SSE, E.ON and Scottish Power in recent weeks.
But the industry has been criticised for being slow to pass on falls in wholesale gas prices, with consumer groups hitting out at the size and timing of cuts.
Most of the recent reductions will not take effect until early spring.
The British Gas cut will take effect on 16 March, while EDF is reducing its prices on March 24.
British Gas said customers will save on average £31 after the move.
It has already cut prices twice since the start of 2015 - in February and August - and said all three reductions together will bring average annual dual fuel energy bills down by £98.
The group has also reduced prices on its fixed tariffs that are open to new customers.
Its cut will not apply to older fixed tariffs no longer on sale, but confirmed customers can switch to current tariffs without charge.
EDF, whose cut will also save customers £31 on average, said costs "beyond our control" limited the size of its reduction.
Beatrice Bigois, managing director of customers at EDF Energy, said: "Our prices are under constant review and today's announcement reflects falls in wholesale gas costs.
"There are other costs impacting customers' energy bills that are beyond our control - these increased steadily during 2015."
Rachel Fletcher, Ofgem's senior partner for consumers and competition, said: "These price cuts are a movement in the right direction for loyal customers, but they are dwarfed by the savings available by switching from a standard tariff to a fixed deal.
"You could save more money, up to £300, faster by switching."
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