Bloomberg said the rationing -- in which vehicles with license tag numbers ending in an odd number or any letter or other character can only get gas on odd-numbered dates -- is to begin at 6 a.m. Friday. Tags ending with even numbers or zero can get gas only on even-numbered dates.
"This is not a step that we take lightly," Bloomberg said, "but given the shortage that we will face for the next few weeks and the growing frustrations of New Yorkers, we believe it is the right step."
Similar rationing will be imposed in Nassau and Suffolk counties on Long Island Friday, The New York Times reported.
The newspaper said rationing would apply to most private cars. Commercial vehicles -- including buses, taxis and livery cabs -- as well as emergency vehicles, paratransit vehicles and cars with MD plates -- will be exempt from rationing.
Gov. Chris Christie Saturday ordered odd-even rationing in 12 New Jersey counties.
An estimated 25 percent of New York's 800 gas stations are open, Bloomberg said Thursday.