When gas prices soar, Americans wail. Inevitably Congress launches an “investigation” and discovers-over and over again that by and large prices are the result of market conditions and taxes.

But when prices drop sharply at the pump, as they have lately, consumers cheer, use more gas and have no interest in finding out the reasons. Let’s take a look anyway. Maybe it’ll save some “investigating” next time the pendulum swings.

First, this is not an American phenomenon. Oil prices are diving all over the world, and the reason is, as usual, global.

West Texas Intermediate crude, a benchmark for American markets, is $68 a barrel, about 37 percent below the price last June. Brent crude, often watched on the world markets, is hovering around $70. It was $115 just last July. Good for consumers, bad for producers. And much as we would like to herald an alternative energy takeover, the world economy still hinges on the price of oil.

When prices are high, producing nations like Iran, Russia, Venezuela and Saudi Arabia rake in the money. However, when crude prices drop, those nations must retrench. Today’s plunging price of crude has done far more to damage the economies of Russia and Iran than all the western economic sanctions combined. Venezuela also is in economic crisis.

Here’s where it gets complicated.

One reason for the price drop has been a dramatic increase in production in the United States’ shale oil drilling, often known as fracking. It’s far more expensive than regular extraction, but it has grown to 4 million barrels a day, nearly half of U.S. production, increasing the world supply and lowering prices.

Ironically, the same shale oil drillers responsible for the supply spike are getting hit hardest by the falling prices. (Are you still with us?) That is why the Organization of the Petroleum Exporting Countries), made up primarily of Middle East nations, recently decided not to decrease its production, even though its members are suffering from low prices.

They are willing to accept the short-term pain because they hope low prices will drive the U.S. shale oil producers out of the market. If that happens, prices will soar again.

Higher prices are likely next year anyway; even wealthy nations don’t like to sacrifice profits for long. And Californians are likely to see increases because starting in January, the state’s cap and trade law to reduce greenhouse gas emissions will apply to oil and gas products. This is not a tax, as the industry is claiming; but until producers reduce emissions, they will have to buy credits to keep polluting. They are likely to pass along some or all of the cost at the pump, depending again on the world market.

On the bright side, maybe we’ve saved taxpayers the cost of another duplicative investigation to figure out why prices will be going up.