The Energy Regulatory Commission published the new fuel prices this evening, and drivers did not wait for midnight. Queues formed at petrol stations across the country - people rushing to fill a tank at the old price before the new list took effect at 00:01.

That is an image that says more than any survey of purchasing power.

The numbers

Petrol goes up by 4.50 denars per litre, diesel by 6.50. Eurosuper BS-95 moves from 87 to 91.50 denars. Eurosuper BS-98 will sell at 93.50. Eurodiesel D-E V jumps from 91.50 to 98 denars per litre.

Extra light household heating oil also rises by 6 denars, to 98.50 denars per litre. Heavy fuel oil goes up by 0.188 denars per kilogram and will cost 43.726 denars.

For an average 50-litre tank that means around 225 denars more for petrol and around 325 denars more for diesel compared with last week. The average increase is 4.85 percent.

The calculation behind the decision

The regulator links the change to movements on global markets. Over the period taken into account, reference prices for petrol rose by 8.983 percent, while for diesel the increase was 10.979 percent. The denar's exchange rate against the dollar fell by 0.2247 percent.

The calculation still applies a reduced excise duty - two denars per litre on petrol and four on diesel. Without that relief, in other words, the hit would have been bigger.

One week up, one week down

This is the part worth pausing on. On 10 August petrol was cut by four denars and diesel by eight denars per litre. Exactly one week later, petrol goes up by 4.50 and diesel by 6.50.

With today's decision, a large part of that reduction is effectively cancelled. Seven days on, the driver is almost back where they started - plus a bit.

This is not an error by the regulator; a formula is a formula and the market moves. But for someone filling a tank once a week, this swing means budgeting the monthly cost is guesswork. And that is exactly why there were queues last night - not panic, just simple arithmetic.

The regulator stresses that the set prices are maximums and that retailers may sell for less. How many of them actually do is a question best answered by anyone who regularly reads the boards at the pumps.