There are many technological reasons why modern vehicles are more fuel-efficient than their predecessors. But the technological move that yielded the most mileage for the buck was the adoption of automatic transmissions with more than four gears. Basically, it’s a case of allowing higher vehicle speeds with lower engine speeds, which also aids engine longevity.

This revolution started in earnest in the late aughts with the advent of five- and six-speed transmissions, and has continued so that now there are 10-speed transmissions available.

So if you’re currently considering a used vehicle in that age range, it would behoove you to make sure the vehicle in question is one of the enlightened ones — those fitted with an automatic transmission with at least six gears. (Or maybe even a CVT (continuously variable transmission), but that’s another story, for another day).

What about nine or ten speeds?

One of the world’s premier maker of automatic transmissions, ZF Friedrichshafen of Germany, makes millions of its eight and nine-speed automatic transmissions.

And GM and Ford announced last year started selling nine- and ten-speed automatic transmissions they co-developed. Most new vehicles introduced in the next few years, particularly in the mid- to high-price segments, will surely be packing these eight-, nine-, and ten-speed transmissions.

Not likely. ZF has gone on record saying it believes nine is pretty much all you need, citing that the key is just achieving low-enough engine speeds, and adding more gear ratios after that would only bring complexity, weight, and cost.

But back to the used car market… You can easily find out how many speeds are in a prospective used vehicle’s automatic transmission by looking up its specifications for its particular model year, easily accomplished by consulting that thing called the world wide inter-web.

Another great resource is the Fuel Consumption Guide published online by Natural Resources Canada. If you’re looking for fuel consumption comparisons you’ll probably want to go there anyway, and NRCan’s ratings are always matched to the vehicle’s engine size and transmission type (manual or automatic, number of gears).

But just to hone down your hunt somewhat, let’s review when some of Canada’s top-selling midsize nameplates made the switch to a multi-speed automatic.

The Chevrolet Camaro and Ford F-150 are very different vehicles from competing companies, but what they have in common is they were the first cars to use the 10-speed that these two manufacturers collaborated on.

Honda was next to the 10-speed party with its Odyssey minivan and Accord sedan.

Ford largely skipped over eight- and nine-speed gearboxes, but GM has loads of them, as do vehicles from countless other carmakers.

The transmission is obviously not the vehicle’s whole fuel-efficiency story. The whole story can be easily ascertained by simply comparing overall fuel consumption ratings. But a multi-speed transmission is where the future it going, and when you’re shopping in the used marketplace, you might as well grab as much future as you can.