But experts say it will take five to 10 years for these alternatives to take root, given the capacity challenge for an auto industry that is adding 65 million new cars a year to a fleet of 1 billion.
In the meantime, car and parts makers, oil companies and even electricity generators are left guessing which way motorists will turn and what technology will win.
"We don't know at the moment whether it's battery-based electricity technology or sustainable biofuels that will be successful," said James Smith, chairman of Shell UK, speaking at a climate change seminar hosted by Reuters.
"The strategic issues confronting us are very significant."
A range of options will emerge as motorists pick between "plug-in" electric cars, longer-range gasoline-electric "hybrids," or simply downsized, more efficient gasoline and diesel models, and as governments, worried by global warming and energy security, give more or less support for biofuels.
Hybrid vehicles, which have both a conventional internal combustion engine and electric motor and battery, are already popular. Toyota Motor has sold 1.5 million Prius hybrids since 1997 and it wants hybrids to reach one tenth of its total sales by 2011.
In a hybrid, the electric battery and motor aid stop-start city driving, while the gasoline engine allows longer trips, together cutting energy use and carbon emissions.
Hybrids accounted for 3 percent of U.S. car sales in 2007. Makers absorb most of the extra $5,000 (2,500 pounds) engine cost, leaving the street price only $1000 to $2000 higher.
Hybrids could be "broadly present" in the auto industry in five years, said Vlatko Vlatkovic, head of electrification research at GE, which has much to gain from widespread electrification of road transport.
Paul Nieuwenhuis, automotive researcher at Cardiff University in Wales, said that hybrids like the Prius are soon likely to be overtaken by plug-in hybrids, which will have the extra option to charge from the grid.
General Motors wants its plug-in hybrid, the Chevy Volt, to reach showrooms in 2010. European brands including Mercedes, Volkswagen and BMW and Japan's Honda plan rivals.
Pure plug-in electric cars, meanwhile, have no combustion engine at all and have struggled to shake off a quirky image - with tiny sales of fabulous cars at prohibitive prices or else economy-sized "golf carts," both with limited range.
