Shares open at A$2.43 vs issue price of A$2.50 IPO was priced at...

• Shares open at A$2.43 vs issue price of A$2.50
• IPO was priced at bottom of float range

(Adds company details, Caltex comparison)

MELBOURNE, July 13 (Reuters) - Shares in oil refiner and marketer Viva Energy (VEA) debuted on Friday at a 3 percent discount to their issue price in Australia's biggest initial public offering in nearly four years.

The stock opened at A$2.43, below the issue price of A$2.50 after its owners, led by global energy trader Vitol , raised A$2.65 billion ($1.96 billion) selling 55 percent of the company.

The float was priced at the bottom of the bidding range at 13.1 times forecast net profit for the year to June 2019, a slight discount to rival Caltex Australia Ltd (CTX) . Caltex was also trading lower on Friday, down 0.2 percent.

Vitol and its unnamed partners built Viva Energy after buying Royal Dutch Shell's former refinery in Geelong near Melbourne and its petrol stations in Australia for $2.6 billion in 2014.

They have since spent more than A$1 billion improving the business, including buying Shell's jet fuel operations, expanding its petrol station network, and acquiring a 50 percent stake in independent fuel retailer Liberty Oil.

The IPO was run by Bank of America Merrill Lynch, Deutsche Bank and UBS.