LPG had its chance here in Australia in the 2000's, but it didn't work out [1]. Subsidised conversions were offered back then, which many people took up on their 80's+90's model cars, but it probably led to the early demise of many of those cars. By the late 2000's there were factory cars selling with LPG "gas" systems, but they weren't as good as the petrol variants [2]. By 2011 you could get "liquid injection" models, which were as good [3]. But like the first article states, people with "large" cars were shifting to SUV's and dual cabs by that stage, and a lot of them were 4cyl petrol/petrol-turbo/hybrid/turbo-diesel, so their fuel efficiency was comparatively decent.

Also in 2011, the government introduced fuel-tax on to LPG, which it had been exempt/discounted on previously. So the price went up, and all of a sudden it wasn't as economical. So that put it in to a death-spiral, especially when many servo's started getting rid of it due to low demand. Now people with LPG cars have "range anxiety" [4]. Where I live (Perth, Western Australia), you are basically stuck in the metro area if you are LPG only. It also means there's a ton of ~2008-2012 LPG Falcons for sale second-hand at good price, but no one wants to buy them.

Out of curiosity, I just went and looked up some data for where I live - the Perth metro (source [5]);

  Year  Month  Fuel  c/L avg  Servos  $cost / 100km for Ford Falcon sedan (UNO)
  -----------------------------------------------------------------------
  2010  Dec    LPG     69.4   216     @ 15L = $10.4  (gas model)
               ULP    128.0   298     @ 10L = $12.8  (petrol model)
  2019  Dec    LPG     89.0   147     @ 15L = $13.4  (gas model)
               LPG     89.0   147     @ 12L = $10.7  (LPi model)
               ULP    144.9   387     @ 10L = $14.5  (petrol model)
  2024  Dec    LPG    133.9    46     @ 12L = $16.1  (LPi model)
               ULP    172.7   436     @ 10L = $17.3  (petrol model)
               ULP    172.7   436     @  6L = $10.4  (Falcon Ecoboost 4cyl 2L turbo)
               Dsl    178.5   437     @  9L = $16.1  (Ford Territory SUV 2.7L TD)

[1] https://www.fleetcare.com.au/news-fleettorque/fuel-cards/wha... [2] https://www.smh.com.au/national/running-the-rule-over-lpg-op... [3] https://www.drive.com.au/reviews/ford-falcon-ecolpi-lpg-revi... [4] https://www.abc.net.au/news/2023-04-19/lpg-cars-disappearing... [5] https://www.fuelwatch.wa.gov.au/retail/historic