Odd-even gas rationing has taken effect in New York City, but it's sparking some confusion and frustration at the pump.

In a dramatic move to shorten gas lines, Mayor Michael Bloomberg followed in New Jersey's footsteps and announced that drivers will only be allowed to fill up on certain days. Plates ending in an odd number or letter have the green light for odd-numbered calendar dates, while those whose plates end in an even number or zero can get gas on even days.

Most drivers say they've noticed shorter lines, but many didn't know rationing had taken effect. One woman says she was kicked off a line because it wasn't her day, but another man said patrolling officers didn't notice him filling up even though it wasn't his turn.

Bloomberg says that only a quarter of the city's gas stations are open. Some are still closed because they don't have power, and others don't have fuel because of delivery problems.

Gas rationing: What you need to knowVIDEO: Mayor Bloomberg on gas rationing, outages, mass transit