Londonderry is the most expensive place in Northern Ireland to buy petrol, it has been claimed.
Sinn Fein's Martina Anderson said the the Consumer Council had also found that Derry was the second most expensive place for home heating oil.
She called for fuel suppliers to engage with the NI, London and Dublin governments over the situation.
"These kind of price increases impact significantly upon hard-working families and businesses of all sizes."
"The Consumer Council last week revealed that in May 2009, it cost £48.78 to fill a car with a 50 litre tank with petrol - and £50.99 with diesel," said Ms Anderson.
"At the beginning of May 2010, it is £12.00 more expensive to fill with petrol and £10.57 for diesel.
"There is a huge disparity between what people in the North of Ireland pay at the pumps compared with those in other parts of these islands.
"For example, petrol is currently almost 6p a litre more expensive than it is in the South while diesel is more than 15p per litre."
Speaking in the Assembly on Monday, Ms Anderson said this was particularly worrying in rural areas where people had to rely on private transport.
"What is needed now is direct discussions between the fuel suppliers and the Belfast, Dublin and London administrations towards reducing the burden on the consumer here," she added.
"Pressure must also be maintained on energy companies to introduce social tariffs as a means to reduce fuel bills for vulnerable customers.
"Fuel poverty in the North is estimated to be at 40% - compared with the 2006 levels in England of 12%, 23% in Scotland and 21% in Wales."