Enlarge Wieck NYC taxi drivers are supposed to shift to hybrids, like this Ford Escape, when an Oct. 1 mandate kicks in. DETROIT  This fall, New York City yellow taxis will start going green as fleet owners have to buy hybrids to replace the old Crown Victorias as they are retired. The city's decision to mandate the move from an all-gas taxi fleet to a gas-electric hybrid fleet has received much applause, but as the effective date approaches, there's a worry: Inventories of hybrids have dried up across the country as gas prices skyrocket, leaving fleet owners to wonder whether they'll be able to buy hybrids for taxis when they need them. Jesse Toprak, chief market analyst for consumer website Edmunds.com, says there aren't enough hybrids on the market to satisfy another huge leap in demand. "Not even close. Consumers have been on waiting lists for months, and even they can't get one," he says. And the ones available will be spread around. "From the auto manufacturers' viewpoint, they need to balance where the supply goes, because they don't want to irritate the customers who have been waiting for them." New York City's mandate for new yellow taxis takes effect Oct. 1 and is intended to transition the fleet to cars that get 25 miles per gallon or more in city driving. For now, only hybrids can do that. By law, NYC fleet operators can use a vehicle as a taxi for three years before it must be replaced. After the deadline, the new cabs will have to be one of eight approved hybrids. About 3,000 of the 13,000 NYC yellow taxis are replaced each year. There are some hybrid taxis around the U.S., but no other city mandates their use. Chicago recently ordered taxi fleets to have one hybrid vehicle. Matthew Daus, commissioner of New York's Taxi and Limousine Commission, says higher-mileage vehicles eventually will cut 500,000 tons of greenhouse gas emissions a year. He's proud New York is making the move and says he expects San Francisco, Seattle, Chicago, Houston, Boston and possibly London to follow suit shortly. "This is the right time for cities to be planning ahead to help the environment," he says. Ronald Sherman, a fleet owner and president of the Metropolitan Taxicab Board of Trade, says he's not just worried about getting hybrids, but also about buying replacement parts when something breaks. "It's a twofold problem," he says. "Our industry moves a million people a day. I don't know what we're going to do if we can't get them in time." The automakers are trying to help. Earlier this week, Mayor Michael Bloomberg announced that Nissan, General Motors and Ford will provide 300 hybrids a month. Nissan will provide the bulk of them, with 200 Altimas for taxi fleets; Ford and GM each will provide 50. Toyota, which makes four of the eight vehicles on New York's approved-cars list, says it doesn't yet support its cars for use as taxis. So rather than buying vehicles through a fleet program, taxi operators have to get in line like any other customer for a Toyota. Supplies of its hybrids are short: There are only three and four days' worth, respectively, of Prius sedans and Camry hybrids on dealer lots. Tom Voll, field fleet manager for Toyota, says the automaker is doing what it can to help out taxi drivers, but gas prices are making it hard to keep up with demand. "Several months ago, there was reasonable availability for consumers and fleets to buy from dealer stock," he says. But with the rapid consumer shift toward hybrids, "Demand has increased significantly. As a result, our ability to fill demand is constrained." Daus says he's confident the transition to a hybrid fleet will be smooth. His advice to fleet operators worried about dwindling supplies? "Have faith and be proactive," Daus says. "Get out there and order those vehicles now. You know what you need to do. Shop around, get the best deal you can, but do it now." Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more