The price of unleaded fuel reached a high of 149.9c per litre yesterday, 10c higher than in Sydney and almost 20c dearer than Melbourne.

Canberra also had the second-highest minimum price in the country, with its cheapest bowser hitting 141.9c behind Brisbane's 142.9c.

The spike comes despite the Australian dollar remaining high, with yesterday's market placing it at a heightened value of $US1.07 around 2pm.

CommSec chief economist Craig James said this would usually put downward pressure on the market, but the high price of fuel in Singapore had cancelled out any benefits.

''If you look at the Aussie dollar it has risen from 101.5 at the end of December to 107.7 [and] ordinarily, that would lead to a lower cost in fuel,'' he said.

''But at the same time we've seen Singapore's gas price move from $1.11 at the end of last year to about $1.33 now.

''Normally the two would work hand in hand but unfortunately, the Singaporean gas price growth has been greater than the rise in the Aussie dollar so it has had a greater effect.''

But Mr James said this did not explain why Canberra's prices were so much higher than the rest of the country.

The Australian Institute of Petroleum's latest weekly report, for the seven days leading up to February 12, shows Canberra's current weekly average fuel cost was 149.1c compared to 140.5c in Sydney.

The national metropolitan average for the same period was 140.9c.

Mr James said national petrol prices had risen about 2c over the past few weeks because of changes in the wholesale price but that Canberra servos had jacked up their prices at the end of January for no apparent reason. ''If you have a look at the [AIP] price chart for January it shows an upward kick in the price from about $1.40 a litre to about $1.49, and it has basically held from $1.48 to $1.50 ever since,'' he said.

''There is nothing to explain that upward kick. It may have been that prices had been artificially low for too long but Canberra is not usually higher than the national average, so even that doesn't make sense.''

NRMA ACT and Southern Region director Alan Evans said the trend was nothing new for Canberra.

He said capital city motorists had been charged exorbitant prices for years because the city was ''an island in the middle of NSW''.

''They know that in Canberra and Queanbeyan you have to drive a decent distance to get cheap petrol, whereas Sydney has a lot more competition,'' he said.

''In Canberra the market is dominated by the two major food chain servos. We've only got a few small independents, so there isn't that competition.

''Often you'll find places like Yass have lower prices than Canberra.''