For 18 weeks in a row, gas prices have been falling in Massachusetts and much of New England, but between each state’s cheapest and most expensive gas, you may see a spread of 60, 70 or 80 cents per gallon.

For business people like Valerie LaCount of Washington Park Florist in Chelsea, Massachusetts, consistently finding the cheapest gas is critical to the bottom line – especially for a flower business whose delivery people drive 100,000 miles a year.

Along with gorgeous roses and lilies, one of her best recent finds is a smartphone comparison shopping app from GasBuddy.com, which also operates as BostonGasPrices.com, which shows the prices of gas station by station as reported and confirmed by GasBuddy members.

“Initially, it shows up by distance, but if you hit this right at the bottom, it will then sort by price, so it brings down to whoever the lowest gas prices are in the area,’’ LaCount explained as she showed us how she uses the app.

The service helped her find the current holy grail of petroleum retailing -- $1.99 a gallon gas – at a station in Boston’s Roslindale neighborhood when she was making a delivery near there recently.

“It was amazing, and if it hadn’t had been for GasBuddy, it never would have happened,’’ LaCount said.

Mary Maguire of AAA Northeast, which runs its own weekly and daily price surveys, said those tools, GasBuddy, and others exemplify one of the most important angles to shopping for gas deals: Knowing and recognizing when you’re looking at a bad, good, or terrific price of gas when you pull into a station.

“Educate yourself about the low end of the price range,’’ Maguire said. “Knowing and shopping the low end of that range is extremely important.’’ Buying gas at stations that offer lower prices is one way motorists can fuel a virtuous price cycle, Maguire said. “Some retailers drop their prices far faster than others, and you want to give your business to the most competitive retailers. It not only saves you money, but they deserve your business if they're going to provide you with competitive pricing,’’ Maguire said.

In terms of whether there are especially good times or days of the week to shop for gas, AAA’s surveys confirm that those “Terrific Tuesday” and “Wacky (or Wild) Wednesday” offers do reflect a demand-and-supply price response.

“A lot of people tend to buy gasoline on Friday in preparation for the weekend and being out and about, doing some weekend traveling or a weekend trip, and a lot of people tend to buy gas on Sunday and Monday in preparation for their commute to work,’’ Maguire said. And so, surveys find, “a lot of retailers drop their prices mid-week when people tend to be buying a little bit less gasoline.’’

Valerie LaCount said she’s seen much the same thing as she’s followed GasBuddy day in and day out. But maybe her single most important piece of advice as an educated consumer: “Do not drive out of your way to fill up, because you lose,’’ LaCount said. “If you're saving two or three cents a gallon, even if it's 20 gallons, you're talking about 40 or 60 cents, and you've blown that by the time you've gotten wherever you're going. So stay on your route. Unless you're talking about a 20, 30 cent difference a gallon, it's not worth it.’’

With video editor Bob Leone, videographer Daniel J. Ferrigan, and assisting videographer Bob Ricci