Over the past year, gasoline has been taking more and more out of your wallet. If you’re like most Americans,  you now spend more than $1,000 at the pump annually. But are you spending it wisely? To become a smart consumer, you need to know the three Ws—the who, what and when—of buying gas.

Whose Name Is on the Pump?

Most people believe that all gasolines are pretty much the same and that the name on the pump doesn’t matter much. What’s more, those perceptions are spreading. According to industry statistics, only about 30 percent of today’s drivers remain loyal to a particular brand, compared with 38 percent back in 1995.

Two trends have eroded brand loyalty. First, there’s stricter government regulation. When Congress passed the Clean Air Act in 1990, it gave the U.S. Environmental Protection Agency the authority to set minimum standards for gasoline sold in different seasons in different parts of the country. Those standards took effect throughout the ’90s and now regulate everything from a gasoline’s volatility (how fast it evaporates) to the amount of detergent added to keep fuel injectors clean. Basically, they offer not only environmental protection, but consumer protection as well. Minimum standards have made truly bad gas truly scarce.

Second, gasoline companies have shied away from trying to distinguish their products from their competitors’ based on quality or performance comparisons. In recent years, the Federal Trade Commission has slapped several big-name oil companies with complaints about misleading or unsubstantiated ads. “Exxon gasoline keeps your engine cleaner…so it can help drive down maintenance costs,” said one ad. “Amoco Ultimate is the only premium refined an extra step to remove harmful impurities…for unsurpassed performance and a cleaner environment,” said another. The government forced the companies to pull these and similar ads because they didn’t have the scientific evidence to back them up.

When consumers believe that gasoline is gasoline is gasoline—and oil companies give up trying to prove otherwise—it becomes harder to lure motorists into higher-priced, brand-name stations. In fact, experts point out that all base gasolines are pretty much the same. Trucks from several companies usually fill up at the same terminals, and the various proprietary additives are “splash-blended” in the truck. So there are differences between various brands, say the experts, but they don’t matter much in engine performance; as a general rule of thumb, the cheapest is the best.

What Grade for the Tank?

So-called “premium” gas accounts for 1 out of every 5 gallons pumped in the U.S.—even though only about 10 percent of the cars on the road require higher octane. Either those cars log an awful lot of miles, or a lot of people are wasting money.

The myths about premium gas begin with its name. Premium isn’t really “superior” gas, as the word implies; it merely has the highest octane. Octane doesn’t measure how good a gas is, but rather how slowly it burns: The higher the octane, the slower the burn.

Why is burn rate such a big deal? In some cases, gas ignites too quickly in the cylinders, a condition know as “engine knock.” You hear rattling or pinging under the hood whenever the engine works hard—usually when you accelerate or climb a hill. A little knocking every once in a while is nothing to worry about. Persistent, heavy knocking, however, can seriously damage your engine. Naturally, the simplest way to stop gasoline from burning prematurely is to get slower-burning (higher-octane) gas.

Some cars with high-performance engines really need high-octane, slow-burning gas; their owner’s manuals will say so. In a few cases, older cars need higher-octane gas, too, only when enough carbon deposits build up inside the combustion chamber to actually change the volume of the cylinders and therefore the compression ratio. (Cleaner-burning fuels and knock sensors in modern engines have made this problem rare, though.)

Basically, if your owner’s manual doesn’t recommend high octane and you don’t hear funny noises from your engine, then regular unleaded will work just fine. You won’t get better mileage, more power or improved performance from premium. If you do hear a little knocking, then move up the scale gradually, searching for the lowest octane that will eliminate the noise.

When Do You Fill Up?

Many people put off fill-ups as long as possible; stopping at a gas station ranks as one of the most boring, time-consuming chores you face. But there are a couple of pretty good reasons not to run the needle right down to E.

One is condensation. Water vapor from the atmosphere condenses on the inside of your gas tank, the same way droplets form around a cold beer mug on a humid day. Over time, in winter, enough water may collect to form ice crystals, which can impede the flow of fuel in the lines. Experts emphasize that condensation isn’t really as big a problem now as it once was; thanks to pollution controls, today’s cars have closed fuel systems in which internal vapor pressure keeps out moist ambient air.

Prudence, however, is a better reason to keep the tank around a quarter full. You just never know how accurate the gas gauge is, and the only real way to test it is to run out of gas.

After all, the only thing more boring than driving into a gas station is walking to one.