In Europe, Volvo Trucks has an diesel-LNG dual fuel truck that was field-tested by a few fleets in the UK and in Sweden in 2010. Rather than direct-injecting natural gas into the combustion chamber, Volvo uses port injection at the intake manifold to produce a premixed natural gas fuel mixture that is ignited by a pilot injection from the diesel injectors. They plan to have limited numbers of diesel-LNG available for sale starting in 2011. Please remember that "gas" used in the videos below refers to methane rather than gasoline.
Please notice in the first video (by TheAutoChannel) that Volvo also uses a two line fill procedure (see video 0:22 to 0:32), which has significant advantages over single line fills to eliminate vehicular LNG issues. The vent line is the orange line to the right of the fill line and you can see a second operator replacing this line on the LNG dispenser when refueling is completed.