Bonn, Germany  - Germany's anti-monopoly watchdog, the Federal Cartel Office, launched an inquiry Wednesday into motor-fuel companies to establish whether there were any "distortions" to free competition in the sector.

The sectoral study responds to outrage among German motorists that pump prices always seem to spike just before half the nation packs the car to depart on long weekends or summer holidays.

The office in Bonn said it acted after receiving many letters from consumers.

It said the inquiry had also been prompted by complaints from the owners of independent petrol stations that they were sometimes charged wholesale prices higher than the main brands' pump prices.

A report would be compiled by the end of the year. If any evidence were found of breaches to competition law, the Cartel Office would act.

Five international majors sell 73 per cent of Germany's motor fuel: Shell, BP, ConocoPhillips, ExxonMobil and Total. (dpa)