Saga found the average annual spend on fuel bills for the over-65s soared to 1,355 pounds last year.
Older people have seen their energy bills more than double since 2005, according to research.
The average annual spend on fuel bills for the over-65s soared to £1,355.90 last year, amounting to more than twice as much as the average of £668.98 in 2005, Saga's analysis found.
Across the UK, some 12.9 million pensioners spent an estimated £17.4 billion on electricity and fuel bills in 2012, Saga said.
It added that its research among the over-50s showed almost three in five (58%) are worried about heating costs this winter and more than a third (35%) are already struggling with heating bills.
Its figures do not take into account the effects of a recent string of price hikes announced by energy companies, pushing costs up further this winter.
Research by MoneySupermarket.com found earlier this month that energy customers on standard tariffs could be facing average quarterly bills of £530 in the coming months. Consumers typically use around 40% of their annual energy consumption during winter.
Saga has argued that older people are disproportionately affected by increases to living costs, as they are often trying to live off a fixed income or savings.
The findings come after Prudential said this week that people planning to retire this year expect to be living off the lowest average incomes recorded in six years. This year's retirees expect to have a typical annual income of £15,300, making them around £3,400 a year worse off than workers who retired in 2008, Prudential said.
Financial information website Moneyfacts also reported this week that annuity rates, which set the size of someone's retirement income, plunged over 2012 for men at their steepest rate in 14 years.
However, retirees were given some welcome news on Thursday when the UK's top statistician announced that a key measure of inflation which is often linked to retirement incomes should remain unchanged.