The volatility of oil refining and the private equity-like ownership of Viva Energy have emerged as early factors playing on the minds of potential investors in what is set to be the country's biggest IPO for more than three years.

Portfolio managers have started ploughing through the research released last week by sponsor brokers Bank of America Merril Lynch, Deutsche Bank and UBS, which value the fuels refiner and marketer between $4.3 billion and $6.2 billion.