AT today’s prices, it’s understandable that drivers accustomed to filling their gas tanks with premium would be looking for ways to ease the financial pain.

Some relief may be as close as their next fill-up. Switching from premium-grade to regular unleaded can save several dollars on each tankful, given an average price difference of about 30 cents a gallon, according to end-of-July figures compiled by AAA.

While using gasoline that carried a lower octane rating than the engine required was once a sure path to disaster, that is no longer the case. Nearly all automobiles sold in the United States since the 1990s will happily run on regular-grade 87-octane gasoline without causing engine damage, a benefit of the electronic controls that now manage all engine functions.

The octane number posted on the pump is a measure of a gasoline blend’s resistance to a condition called knocking. The knocking sound  a rattling noise made by an engine under load, familiar to drivers of older cars  is a result of out-of-control combustion, the mixture of air and fuel burning erratically. The explosion rings the metal of the engine block like a bell.