PORTLAND, Ore. (AP) -- The Northwest Power and Conservation Council says that plug-in hybrid electric vehicles could help make the nation's electric power system more efficient in addition to reducing greenhouse gas emissions.

The Portland-based regional council says that even though the vehicles could boost overall demand for electricity, most of them would be charged at night, when demand is low.

The council is reviewing a study that says nearly half to three-fourths of all the cars and light trucks in the nation could be replaced by plug-in hybrids without adding new power plants or transmission lines.

The study says the overall energy savings could cut oil imports in half and reduce carbon dioxide emissions by a fourth.