Police arrested 181 Romanian nationals in the first half of this year for such crimes, compared to just 136 Norwegian nationals, according to the Dagbladet newspaper.
"There is no doubt that much of the increase in crime is down to foreign gangs," Geir Ellefsen of the Oslo police told the newspaper. "The special feature of this year is that we have arrested more Romanian nationals for theft than Norwegians."
The statistics are likely to fuel resentment against the Roma who have camped out in Oslo in recent years, although the crime wave predicted last year after their arrival has not materialized.
The number of house burglaries in June and July dropped by 42.5 percent compared with the same months last year, while pickpocketing has declined by over 20 percent since last year.