The 2017 BMW i3 REX (94 Amp-hour battery) achieves 35 MPG combined, a somewhat misleading figure at first glance. This isn’t your typical gasoline-powered car, and it isn’t strictly an EV either. That mixed number reflects electric range meeting gasoline backup, catering to buyers who prioritize electric driving but need the security of extended range on occasion.

City and highway performance

The EPA estimates the i3 REX at 36 MPG in the city and 33 MPG on the highway. However, these numbers only matter when the Range Extender (REX), a small 0.6L 2-cylinder engine, is actively supplementing the battery.

The electric range, typically 90-110 miles in real-world driving, is where the i3 is best. For urban commuters with predictable daily routes, the gasoline engine might rarely activate, resulting in significantly better overall “fuel economy” than the EPA suggests. On longer trips, however, the REX activates, providing a safety net against range anxiety, albeit with the MPG figures listed on the window sticker.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2017 BMW i3 REX at $1,650. This figure is based on driving 15,000 miles per year and using national average fuel prices. Of course, the actual fuel cost for an individual i3 REX owner will vary significantly depending on their driving habits and the percentage of miles driven on electricity versus gasoline.

Someone who primarily uses the i3 for short commutes and charges it regularly might spend considerably less than $1,650 per year on fuel. However, those who frequently rely on the range extender for longer journeys will likely find this estimate to be more accurate. The $1,650 includes only the cost of gasoline; electricity is calculated separately.

Real-world expectations

Don’t be fooled, the i3 REX isn’t about achieving Prius-level fuel economy when running on gasoline. The REX engine is designed to maintain range, not maximize efficiency. Think of the 35 MPG as an emergency fallback plan. Owners who maximize their electric driving will see far better results, potentially using only a few gallons of gasoline per month.

Conversely, continuous use of the REX will yield results closer to the EPA estimates, but that defeats the purpose of owning an i3.

How it compares

Compared to a Toyota Prius (52 MPG combined), the i3 REX’s gasoline MPG is not as good. However, the Prius doesn’t offer the pure electric driving experience that the i3 does. A Chevrolet Volt (42 MPG combined, plus electric range) presents a closer rival, offering a similar plug-in hybrid approach with a longer electric range.

Other small gasoline-only cars, like the Honda Fit (33 MPG combined), achieve similar fuel economy to the i3 REX while running on the gasoline engine, but lack the electric capability altogether. Ultimately, the i3 REX buyer isn’t solely focused on MPG; they are willing to accept a less-than-stellar gasoline MPG in exchange for electric driving and range security. Prospective buyers can find all BMW fuel economy data on our site.

Tips to maximize efficiency

Prioritize charging. This seems obvious, but consistently plugging in the i3 REX whenever possible is the single most effective way to minimize gasoline consumption. Take advantage of Level 2 charging at home or public charging stations to replenish the battery faster and reduce reliance on the range extender.

Drive conservatively. Aggressive acceleration and high speeds drain the battery and force the REX to engage sooner. Smooth, steady driving not only extends the electric range but also improves the fuel economy when the range extender is active.

Use the i3’s regenerative braking system. The “one-pedal driving” feature allows you to decelerate by simply lifting off the accelerator, converting kinetic energy back into electricity. Mastering this technique significantly increases energy efficiency, especially in city driving. Experiment with different regen modes to find what suits your driving style best.

Plan your routes strategically. Before embarking on longer journeys, carefully map out charging locations along your route. This allows you to maximize electric driving between charges and minimize the need to engage the range extender, optimizing your overall fuel consumption. Remember to check the availability of public charging points beforehand.

Consider a larger battery in a newer i3, or the fully electric i3 without a REX unit. If you find that the REX unit is used often, consider going fully electric to save money on fuel and maintenance. See more about I3 MPG across all years on our site.