Electricity customers in south Wales pay up to 10% more compared to people in England, according to a report by Energywatch.
Energy consumers in north Wales pay on average 4% more and Energywatch is concerned that more than 270,000 households were classed as "fuel poor".
The results of the report are to be discussed today by the Welsh Assembly sustainability committee.
Chair of the committee, Mick Bates, said : "Fuel poverty and the impact of increasing fuel prices mean that there are many people cold this winter. I am looking forward to hearing the energywatch research findings in this area, and I am very pleased that the energy companies have agreed to give evidence."
Since the beginning of 2008 all major energy suppliers have increased their prices by an average 15%.
Energywatch believes that the latest round of price increases has increased the number of households in fuel poverty to around 4.5 million nationally, a rise of around 500,000.
(CD/JM)
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