UK - Pension scheme liabilities for FTSE 100 companies increased by 1.5% last year, as longevity expectations increased for the fourth year running, according to Mercer.
Mercer said current pensioners were expected to live five months longer and that future retirees were estimated to live seven months longer.
The consultancy's head of pension accounting Warren Singer said the accounting assumptions made by companies impacted strongly on their liabilities.
"Overall, changes in accounting assumptions have increased the median FTSE 100 company's UK pension liabilities by around 20%," he said.
"The wide range of views taken by companies on accounting assumptions, in the face of economic uncertainty, makes it very difficult for users of accounts to compare pension accounting disclosures."
According to Mercer, differences range from the estimated rate of inflation, which ranges from 3.1% a year to 3.9% a year.
Additionally, companies were divided over how much to expect from equities, with long-term estimates on return starting at just under 7%, while other companies expected as much as 9.2%.
Singer said there was no single right approach to these assumptions.
"Therefore, the IASB is proposing to address the diversity of views by requiring additional disclosure information, such as the sensitivities of liabilities to assumption changes," he added.
The consultancy analysed the returns of 44 FTSE 100 companies for its survey.
In other news, figures released by F&C Asset Management show that pension funds have shied away from inflation hedging amid fears of a double-dip recession and possible deflation.
Schemes reduced their inflation hedging by almost a third in the second quarter of this year, albeit from an usually high level in the first three months of 2010.
Figures for the company's second-quarter LDI survey showed that, over the last three months, inflation hedging roughly fell in line with rates during 2008, following a year of uncertainty in 2009.
Alex Soulsby, derivatives fund manager at F&C, said recent months had seen uncertainty surrounding the demand for inflation hedging with retail price index products, after the UK government announced pensions would be linked to the consumer price index.
"However," he added, "the index-linked gilt syndication on 27 July was attractively priced, and demand was much larger than expected.
"This seems to suggest these concerns are exaggerated."