American consumers are going to enjoy a more bountiful Christmas this year, thanks in part to a most unlikely source: Saudi Arabia.

The steepening drop in gasoline prices in recent weeks — spurred by soaring domestic energy production and Saudi discounts for crude oil at a time of faltering global demand — is set to provide the United States economy with a multibillion-dollar boost through the holiday season and beyond.

The windfall, experts say, comes at a critical moment, with the American economy on the upswing but facing headwinds from other quarters, including weaker exports because of slow growth overseas. Gas prices recently dropped below $3 a gallon for the first time since 2010, while crude oil prices have fallen by more than $25 a barrel since midsummer, settling on Thursday just above $74.

“If oil prices stay between $75 and $95 a barrel, we would see the kind of stimulus package that the Federal Reserve or Congress could never do,” said Douglas R. Oberhelman, the chief executive of Caterpillar, the multinational maker of heavy construction equipment.