Rural authorities which tend to have older and less deprived populations receive lower grant allocations, according to the study.
They spend less on social care, charge more for home care and allocate lower personal budgets than local authorities serving urban, younger and more deprived populations.
Commissioned by the Commission for Rural Communities, the study was carried out by Sheena Asthana, Professor of Health Policy at Plymouth University.
The full document – Variations in access to social care for vulnerable older people in England: is there a rural dimension? – can be downloaded here.
The commission said the report made a powerful case for the government to re-consider the balance of funding for social care between urban and rural local authorities.
Variations in social care expenditure on older people were very significant, it said.
At one extreme, Tower Hamlets spent £2552 on each person aged 65+ in 2009-10 – nearly five times more than Cornwall (£520).
This reflects a pattern of expenditure across 12 inner London boroughs averaging £1,750 per person aged 65+ compared to just £773 per capita across 27 shire counties.
This huge disparity in social care expenditure should give rise to concerns as to whether the current distribution of resources, expenditure and activity is equitable, said the commission.
Older people living in local authorities which received lower grant allocations were charged significantly more for home care than older people living in well resourced councils
Professor Asthana concludes that these differences in access to social care were likely to be at least partly a function of a flawed national resource allocation formula.
The formula continued to be based on an understanding of prior usage of the services, rather than an understanding of actual need.
"There is evidence to suggest that people with similar care needs are assessed and supported very differently in different places," she said.
"People may assume that statutory funding is distributed according to the needs of the population, but the role that resource allocation may play in reinforcing inequalities in access to social care has rarely been considered."
Commission chairman Stuart Burgess said the research took understanding of social care funding in different areas to a new level.
"The commission will be talking to ministers and senior government officials about ensuring that people in rural communities have fair and equal access to social care services compared to those in urban areas."
The research would inform the commission's forthcoming report into social isolation experienced by older people in rural areas, which is expected to be published soon.