Both Airbus and Boeing now offer aircraft that appear capable of flying non-stop commercial flights from Sydney to London - the "Holy Grail" for Australian carrier Qantas Airways Ltd, Reuters reports.

As long as oil prices don't go much higher than around $70 per barrel, the 20-hour flight can be financially viable, and could be on schedules within five years, aviation experts say.

Airbus has increased the range of its A350-900ULR to 9,700 nautical miles (17,960 kms) from the 8,700 nautical miles announced when it sold the plane to Singapore Airlines in 2015 for delivery next year, a spokesman told Reuters. Including headwinds, the Sydney-London flight is equivalent to 9,600 nautical miles.

"These aircraft, we think, are potentially real goers on these routes," Qantas CEO Alan Joyce told Reuters of the A350-900ULR and the bigger but less advanced Boeing 777-8. "You know from what they have done on other aircraft that Sydney-London and Melbourne-London has real possibility."

For Qantas, a non-stop Sydney-London route that cuts three hours off the flight time would allow it to charge a premium and differentiate its product from the around two dozen other airlines plying the so-called Kangaroo route with stop-offs in Singapore, Dubai and Hong Kong.

The route accounts for only 13 percent of Qantas' international capacity, but carries the prestige QF1 flight number and is important to its global brand.

Qantas could charge around a 20 percent price premium for a non-stop Sydney-London flight as it would attract business and premium leisure travelers wanting to complete the trip as fast as possible, said Rico Merkert, a professor specializing in transport at the University of Sydney's business school.

"It's something that can be presented as a unique selling point for Qantas," he said.