The takeover of Asda by billionaire Blackburn brothers Mohsin and Zuber Issa is being investigated by competition regulators.
Their EG Group and private equity partners TDR Capital bought the supermarket giant from US owners Walmart in a £6.8bn deal in October.
The Competition and Markets Authority (CMA) launched the probe after the European Commission referred the deal.
The brothers said the move was "expected".
The Local Democracy Reporting Service reports the CMA will now look at whether the acquisition will lead to a "substantial lessening of competition", particularly in the petrol forecourt market.
The Issa brothers' EG Group, formerly Euro-Garages, has almost 6,000 petrol stations across the UK and Europe and about 44,000 staff.
The brothers and TDR - which formed a takeover vehicle called Bellis Acquisition Company for the deal - are understood to have requested the European Commission referred the deal to the CMA for review.
"As we expected, the CMA have launched a phase one investigation into the acquisition of Asda following a referral from the European Commission," a spokesman for the Issa brothers and TDR Capital said.
"We are looking forward to working constructively with the CMA to address any questions they may have."
The regulator now has until 18 February to reach a decision on the first stage of its investigation and whether to mount a full-blown probe.
It has set a deadline of 22 December for interested parties to comment.
The pair have committed to keeping Asda's headquarters in Leeds and said they would invest to grow its convenience and online operations.