Sam Boyle is holding one gallon of regular-grade gasoline.

The color of apple juice, it has the hydrocarbon content of 98 tons of buried prehistoric plant matter. It'll ping your credit card for about $3 at our local Southern California prices. And after being combusted in a car engine, two of its 20 pounds of exhausted CO2 will still be inhaled by your descendants—1,500 generations from now.

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Only a few years ago we thought we were running out of gallons like the one Sam's holding. At a technology seminar I attended just five years ago, a nattily dressed oil expert clicked through a harrowing set of graphs. Its chilling climax predicted "Peak Oil"—the moment the world's production would top out, triggering violent price spikes as the oil market's elasticity suddenly snapped. We're doomed!

But we weren't! Prices did, yes, rise. Remember $144 per barrel? Most large SUV buyers don't, apparently. Yet there was barely a peep in that presentation about the thing that's changed everything since: fracking. Although it was experimented with way back in 1947, it's only recently released a deluge of previously inaccessible "tight" shale crude (and environmental controversy), causing prices to collapse and the U.S. to become unexpectedly oil independent—and on the final day of 2015, an exporter again when a tanker of crude departed from Corpus Christi, Texas. A giant tributary to this Niagara-like price plunge has been Saudi Arabia's refusal to throttle its own production (hoping to run the frackers out of business). While Saudi Arabia has maintained a poker face, the game has brought the kingdom to within about five years of insolvency if prices stay below $50 per barrel. Today, Texas Light Sweet is at $30.44. We shall see.

The Chevrolet Volt and Toyota Prius may be precisely what you'll be driving in the not too distant future, regardless of how long those sheiks stick it out.

However, trusty Sam Boyle—who's still holding that beaker of gas (thanks, Sam)—really doesn't care about any of this. His job at our partner company, Emissions Analytics, is to narrowly but scientifically measure how far cars travel in the real world with that gallon. At this moment, he and his assistant, Jesus Flores, have tested a whopping 328 cars and trucks for our Real MPG program. Supported by a 15,000-gallon, chemically stable supply of regular, premium, and diesel grades from our partner, Chevron, the cars are instrumented with a $150,000 gas analyzer and expertly lapped around a tedious 100-mile real-world course. Numbers are crunched and adjustments are made for traffic fluctuations, weather, and air-conditioner use, and once Emissions' London-based chief and statistician, Nick Molden, is satisfied, the results are added to our tally. While there's lots of buzz now about "real-world" testing in the wake of Dieselgate (in Europe, Renault has announced it will publish independent real-world results next to the government scores)—we're already doing this testing. How opportune, then, that the two cars Sam is standing in front of—the all-new 2016 Volt and Prius—are making the biggest gallon-stretching claims out there. Sam may be their worst nightmare. As if they need nightmares.

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The collapse of oil prices has fallen almost directly on the head of hybrid sales, their market share dropping 11 percent in 2015 despite today's otherwise percolating car market. And it has left the rickety math behind hybrids' premium payback time (in the range of $3,500 to $4,600 for the popular ones) now pretty much kaput, too. Yet the revamped Volt and Prius aren't dead men walking. In fact, they may be precisely what you'll be driving in the not too distant future, regardless of how long those sheiks stick it out.

And here's why: Stare at these lines.

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They're going to be way more significant to the automobile's future than oil's spikes and plummets. And see that word regulation? The day after driving the new Kia Niro (an upcoming Prius and Volt competitor, stay tuned for driving impressions), I saw this slide during a presentation at Hyundai/Kia's fuel-cell research facility. On the left is a 49 percent squeeze in U.S. fleet fuel economy, in the middle, the EU's 27 percent noose-tightening on CO2, and on the right, China's 24 percent vice-handle turn on fuel consumption. All three by 2020, and backed-up by stiff penalties. Quicker than you'll say Adam Smith, the automotive market's invisible hand is about to hand a big chunk of its power to planet-spanning governmental edicts. And the only way to thread this needle—technologically—is with hybrids, plug-ins, and eventually battery-electric and fuel-cell cars.

Like it or not, drivetrains such as the Volt's and Prius'—the world's best examples of their respective breeds—are your future. Which better uses our gallon of gas? OK, Sam, pour it in. As Jesus starts his runs, let's dissect the differences.

"This Prius feels like a sports car ... err, wait. Am I really saying this?" Lord no.

"This morning," Christian Seabaugh said before our subjective looping along the Palos Verdes Peninsula in southwestern Los Angeles County, "I had an odd encounter on a long, sweeping freeway on-ramp. There was a Challenger SRT8 on my tail [Oh, Christian …]. I floored it and lost the Challenger [Oh, Christian!]. But once on the freeway, the Dodge pulled next to me and rolled down its passenger window. I expected a middle finger, but strangely enough, I got a thumbs-up." Perhaps the guy didn't recognize the Prius due to its psychedelic new styling.

But what's underneath that bodywork—the debut of Toyota's TNGA chassis—is transformative to the car's feel. As we tackled a twisty bit, I keyed the walkie-talkie. "This Prius feels like a sports car … err, wait. Am I really saying this?" Lord no, not an actual sports car. But its proper rear multilink suspension, lower center of gravity, and lighter weight (450 pounds less than the Volt) had me nipping apexes. Departing them, the tables turned as the Volt's electric motor(s) would surge it away with that notorious EV flood of hydrauliclike torque (fun). Both cars stopped with unpredictable brake feel (not fun), which in the Volt becomes sometimes scary in a sudden I-405 traffic thrombosis due to that extra tonnage. (Boy, that was close.)

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See all 19 photos

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The silver lining (nay, lithium lining) is that the Volt's battery inadvertently imparts great ride quality and quietness. At the same speeds in the Prius, you're twisting up the music's volume; meanwhile, the Volt feels like a very large sedan on a small sedan wheelbase—not a bad thing, actually, for A-to-B just getting there. Yet the Prius, for all its otherworldly technology, is still recognizably Toyota. "The more I drive this Prius," Christian said, "the less I love it and the more I 'like' it. It just leaves me feeling hollow."

Hollow is not a descriptor of the Volt's cabin. Its compromised battery packaging (put the damn thing under the floor!) is the Chevy's 600-pound gorilla—crammed into a 300-pound gorilla cage. "Man, is this back seat tight!" Seabaugh said as he mimed Twister into the second row. "I feel like I'm sitting in the back of a Camaro with the top of my head up against the back glass." (For Christian, every unit of measure is computed via the international ponycar system.)

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Oh, but our story began with Sam and his now-burned gallon of gas. So, Sam, which car sipped it better?

There's good news and there's bad news. His real-world Prius numbers clobbered the EPA's lab tests. Its city-cycle Real MPG of 56.5 mpg toppled the EPA's 54, its 53.4 on the highway stomped EPA's 50, and our combined 55.1 walloped the EPA's 52. Wowee kazowee. That's 7 percent better on the highway and 6 percent better overall.

Even with all the dents the Volt has endured here, the best way to use that gallon is to ultimately not burn it at all.

Bad news: The Volt did the opposite. Although it's a clear step ahead of its first-gen predecessor (tip of the hat), its Real MPG city number in charge-sustaining mode was a lowly 37.5 (compared to the EPA's 43). And although its highway score of 42.4 fractionally betters the EPA's 42, its combined result of 39.6 was short of the government's 42 (a 6 percent miss). Even its EV range ended at 49.9 miles versus the EPA's 53. What's up? Emails to London. Responded Nick Molden:

"While it's better on the highway, there's been no significant improvement on the city cycle. While the Chevy is comparatively immune to AC use and doesn't significantly suffer from aggressive driving, it's noticeably averse to congestion (as normal ICE vehicles are). Maybe it's why city driving performance is much lower than for the Prius."

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About the Prius: "It has a quite different performance profile, and its very low fuel burn rate makes it more sensitive to AC use. Yet the Prius suffers virtually zero penalty in congestion, though it doesn't like being driven aggressively. I suspect its small battery size (now a tiny 0.75-kW-hr lithium-ion) can only boost the acceleration up to a point."

All this triple-underlines why real-world testing is so important.

For a bigger-picture perspective, we spoke with John German of the International Council on Clean Transportation. John's a hybrid-tech veteran and part of the team that unraveled the VW diesel cover-up. "The recent improvements on both the Prius and the Volt are completely consistent with that of each one's previous generation—and why I'm confident that hybrids will go mainstream sometime after 2020," German said. "According to the National Academy of Sciences' 2013 report, 'Transitions to Alternative Vehicles and Fuels,' the cost of hybrids, BEVs, and fuel cell vehicles will converge in the 2030 to 2040 timeframe. However, PHEVs like the Volt will still have a substantial cost penalty due to its two expensive powertrain systems; hybrids will remain more expensive than conventional vehicles, but the cost premium might be down to only $600. With the average hybrid, including hybrid trucks, projected to achieve almost 100 mpg by 2050, putting its real-world fuel economy in the 60-70 mpg range, I have to ask: If your SUV is getting well over 50 mpg, are you really willing to pay a $1,000 to $2,000 premium to plug in for part of your driving?" So not only does the Volt trip on its mileage claims, but its drivetrain's long-term viability is doubtful, too.

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Of course, we are in the here and now, riding toward those 2020 efficiency targets. Carmakers have no choice but to reach for plug-in hybrids. Which is the better here-and-now car then? Both Christian and I preferred the Volt. But if you need a back seat, it's useless. We both loved the Chevy's sense of EV torque—but do you have a charger at home to plug into? The Prius is simply the more significant car. In the big view, it's truly the car of the future, fully functioning today.

Ah, but I haven't answered our question about that gallon, have I? The well-to-wheel distance where the Prius and Volt have produced equal amounts of CO2 is a whopping 115 miles—beyond the length of virtually any daily trip. (Yes, I'm using California's almost extreme-case clean electrical generation, but it's far and away the largest plug-in market.) Up to 50 miles, the Volt produces only 56 percent of the super-efficient Prius' CO2 (the Volt having been in EV mode). And it hangs on to that advantage for another 65 miles until the Toyota overtakes it. Even with all the dents the Volt has endured here, the best way to use that gallon is to ultimately not burn it at all.

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