Overall vehicle fuel efficiency is up in the U.S., helped by increased hybrid and all-electric vehicle adoption and more fuel-efficient gas-powered cars.

Data by online automotive search site iSeeCars.com found nationwide vehicle fuel efficiency is up 11% over the past five years to an average of 27.5 miles per gallon for 1- to 5-year-old cars.

To arrive at the numbers the company said it reviewed fuel efficiency of more than 19 million cars sold in the age segment during the five-year period on both national and state-by-state bases.

It also broke down fuel efficiency by state to determine those that improved the most, Arkansas leading the way with about a 32% improvement, followed by Washington state with a 22% gain, and California with a 19% improvement.

Probably not coincidentally, Arkansas also led in combined hybrid and battery-electric vehicle adoption, up a whopping 875%. Louisiana came in second with 299% growth, and New Jersey is third with 286% improvement.

Though government regulations are fueling part of the increased fuel efficiency, many consumers also want to cut fuel costs, iSeeCars said. That’s not surprising, given overall inflation, including the prices of vehicles themselves.

More rural states leading the way on improved fuel efficiency might seem counterintuitive, especially given their much more limited electric-vehicle charging infrastructure. Meanwhile, California and Washington showed they’re committed to optimum fuel efficiency since their improvement rates stayed high despite already exceeding the national average five years ago, iSeeCars said.

“States like California and Washington are known for their efforts to improve fuel economy and reduce emissions, so it’s not surprising to see them rank well in this area,” said iSeeCars Executive Analyst Karl Brauer in a press release on its research.

“But seeing Arkansas outrank both states in the areas of rising fuel efficiency and growing hybrid and EV market share was something we couldn’t have predicted. Arkansas ranks among the top five states for growth in hybrid, plug-in hybrid, and EV categories, showing rapid adoption across a broad spectrum of fuel-efficient vehicle types.”

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