One group of conference attendees posited that gas nozzles employed a form of ultrasonic mapping in which sound waves were bounced off the interior of the gas tank to determine just how much empty space remained.

PASADENA, CA—In hopes of better understanding a phenomenon that has vexed researchers for decades, hundreds of theoretical scientists have assembled at the California Institute of Technology for the 35th annual symposium on how gas nozzles know when a car’s tank is full, sources said Thursday.


The weeklong academic conference, which draws top experts in quantum physics, pure mathematics, systems theory, and numerous other scientific fields, will feature a variety of interdisciplinary panel discussions and collaborative workshop sessions, as well as dozens of presentations from theorists sharing their ideas about what kind of mechanism could possibly enable a gasoline pump to turn itself off at just the right moment and avoid spilling fuel all over the place.

“All we know for certain is that you leave the nozzle in there for a while, it makes this little popping sound, and then your tank is full. Maybe this is the year we finally figure out why.”


“We’re particularly excited this year, because a team of computational chemists from Poland may have finally cracked the so-called Half-Full Paradox, which has long stumped scientists who have sought to understand how the pump knows when to stop fueling regardless of whether your tank is empty or still has some gas left in it,” said symposium chair professor Marian Reardon, explaining that early scientists who tackled this problem once believed nozzles operated on a timer, but later realized this theory failed to account for tanks that remained partially filled. “We’ll also discuss the pump’s apparent ability to tell whether you’re driving a compact car or a large truck and adjust the volume it dispenses to match the tank size, a complex and puzzling question that no one has yet been able to put forth a convincing theory to explain.”

“All we know for certain is that you leave the nozzle in there for a while, it makes this little popping sound, and then your tank is full,” Reardon continued. “Maybe this is the year we finally figure out why.”


According to symposium organizers, the week will feature a half-day seminar on whether a small camera inside the car’s tank allows gas station attendants to see when it’s time to shut off the pump; a presentation titled “Smart Pumps: Could Computer Chips In Gas Nozzles Recognize The Make And Model Of Every Car?”; and an eagerly anticipated keynote speech from professor Sunita Chowdry, a theoretical physicist who has spent the past two years in residence at a Pump ’N’ Munch filling station in eastern Minnesota.

The conference is also scheduled to include several breakout sessions that will explore how microscopic sensors might be embedded within the nozzle and whether a gas tank’s location on either the driver’s side or passenger’s side provides crucial information to the pump about how much fuel to transfer.


Although many in attendance expressed excitement about a new National Science Foundation program aimed at identifying promising researchers and providing them with tens of millions of dollars in gas money grants to conduct on-site fieldwork—a potentially game-changing source of funding—skeptical sources said they remained wary that any groundbreaking advancements would be made in the near term after having been so frequently disappointed in the past.

“I was here in ’92 when [Oxford mathematician Emil] Bantikov presented his equation that purported to explain why you can still get a few more squeezes of gas into the tank even after the nozzle shuts off,” said professor David Werner, co-chair of the quantum mechanics program at Carnegie Mellon. “For years, he had locked himself away in his lab working on his ‘Extra Splash Theorem,’ until late one night he emerged, overjoyed, with what he thought was a revolutionary discovery. But his formula was quickly disproven, he was shunned from the nozzle community, and his reputation never recovered.”


“So let’s just say I’m not holding my breath for any new breakthroughs,” Werner added.

Still, attendees said the mood at the conference remained generally upbeat, with participants praising a main-stage presentation that examined whether gas stations keep their seemingly unlimited gasoline supply in the awning above the pumps, in the room at the back of the building marked “employees only,” or someplace else entirely. They also reportedly engaged in lively debate during a roundtable discussion about how the little screen on the pump is able to count the gallons of fuel it is dispensing so rapidly and precisely, often to the third decimal place.


Despite this enthusiasm, few of those present appeared to harbor any illusions that the nozzle-shutoff problem would be fully understood for decades or even centuries to come.

“Think about what an incredible and astonishing phenomenon this is: Even if you try to trick the pump after it has finished by removing and then reinserting the nozzle into your gas tank, it will still click itself off when you start pumping again,” said professor Jonathan Lam, a pioneering researcher in the field who is widely admired for a seminal 1993 paper positing that the area beside each fuel pump contains an in-ground scale that weighs every automobile and thereby detects how much gas is required to refill the tank. “No matter what you do, the pump simply won’t let you overfill your tank. Maybe it uses artificial intelligence, maybe satellites, maybe lasers, maybe something we haven’t yet conceived of. But getting back into the car, turning it on, and seeing that needle go right back up to ‘F’—it always reminds me how miraculous it is that the pump dispenses the exact right amount of gas every time.”


“It’s unlikely we’ll have an explanation in my lifetime,” Lam added. “But I feel honored to know I’ve played some small part in laying the groundwork for the generation that one day will find the answer.”

