As early as next year, many Sky Harbor taxi customers may be riding in cabs powered by a range of alternative fuels.

A City Council subcommittee voted last week to recommend a rule that would take effect when the new airport taxi contracts for Phoenix Sky Harbor International Airport are finalized.

Under the new policy, cabs with an airport permit would be required to use one of several alternative fuels.

Gasoline-powered cars - even hybrids like the Toyota Prius - won't be allowed. Although hybrids use less gasoline than regular cars, they don't meet the city's new standard to limit greenhouse-gas emissions and oil use.

The city's proposed alternative-fuel rules impact taxis that have a permit to pick up passengers at the airport. If a traveler hires a taxi elsewhere in the Valley and gets a ride to the airport, that cab can use any kind of fuel.

Phoenix leaders are trying to cut air pollution. Council members on the panel also heard from taxi companies that are concerned that cabs running on compressed natural gas are too costly and may be susceptible to fires.

"Technology is changing," said Councilwoman Maria Baier, who sits on the council's Economy, Commerce and Sustainability Subcommittee.

Now, only one alternative fuel is allowed, and "it would be very dangerous to have what one would call a monopoly," she said later.

The subcommittee unanimously recommended a rule that would give taxi companies more fuel choices. If ultimately approved by the full council, it would also allow the city to explore more fuel options when technology improves.

Under the old airport policy, taxis with airport permits have to be powered by compressed natural gas. Clean Energy is the only firm with CNG fuel pumps for taxis at the airport.

In practice, however, a loophole allowed the airport to make exceptions to the CNG rule. Because of this, many of the airport's 170 airport taxis are powered by gasoline.

Under the new rules, taxicabs would have the choice of using compressed natural gas, liquid propane gas or E85 ethanol fuel.

The new rule also would require that the city enforce the policy with inspections and other methods to make sure that taxicab companies are not using gasoline.

About 40 company executives and others attended Tuesday's subcommittee meeting touting their respective alternative fuels. Clean Energy has provided CNG to airport taxis since 2001, an airport spokeswoman said.

Clean Energy representatives argued that CNG-powered cars have the lowest emissions. Kevin DeMenna, a Phoenix lobbyist for Clean Energy, downplayed the taxi companies' worries about cost and safety.

"The city is going in the wrong direction," DeMenna told the subcommittee, referring to the new policy. He said he believes Clean Energy has the greenest fuel. "That much is clear," he said.