Lukoil Bulgaria is responsible for "artificial" prices of petrol in the country, a research team led by former PM Ivan Kostov has claimed.

There are good reasons to believe the Urals crude oil is imported in Bulgaria at  much higher prices than normal, to the detriment of both households and businesses, Kostov's researchers say in a report [BG] published by the Risk Management Lab, a think-tank based at the New Bulgarian University in Sofia.

Kostov, who served as Prime Minister between 1997 and 2001, is still thought to hold certain influence over the Democrats for Strong Bulgaria (DSB), one of the parties in the right-wing coalition Reformist Bloc which is the junior partner in the government.

The cabinet for its part has been subscribed for analyses prepared by the Risk Management Lab for months.

Lukoil does not provide customs officers with invoices showing the price at which it bought crude, showing instead figures with stock prices for Brent (which for its part is 2.41% more expensive).

Transport expenses paid by the oil giant to bring the crude into Bulgaria have also been written up, the think-tank believes.

All this results in an overall difference of 13.27% in real prices of the crude bought in Russia and those it reported in Bulgaria, the study claims.

Between 2006 and 2014, Lukoil thereby inflated its declared expenses by BGN 763.5 M on a yearly basis, or BGN 6.8717 B for the entire period.

Lukoil is yet to comment on the allegations.