His calculations suggest the deal could provide Viva with more than a 50 per cent market share in Adelaide.

“While divesting some sites may address concentration concerns, it may not address pricing power concerns, given OTR and Coles Express set fuel prices across all their sites,” Allen said.

“[We] remain somewhat cautious that genuine ACCC challenges await.”

Gordon Ramsay, an analyst with the Royal Bank of Canada, also said ACCC concerns loomed as a “potential deal-blocker”.

Macquarie Research, however, does not expect the ACCC issues to be “too material”, noting that Viva has just 43 sites in South Australia and OTR has 15-20 existing sites outside the state.

OTR’s network includes 184 integrated fuel and convenience stores and 31 standalone retail stores. The company generates more than $3 billion of revenue a year and employs about 6500 people.

Viva last week said it intended for OTR to replace Coles Express as its flagship convenience brand “over time”. In a $300 million deal last year, Viva acquired the Coles Express convenience business, which it had previously operated in a joint venture with Coles.

Viva Energy chief executive Scott Wyatt described OTR’s non-fuels retail offering as the “best in the country, possibly one of the best in the world”, with more than 70 per cent of its profits coming from non-fuel sales.

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