The single thing most likely to increase fuel consumption is aggressive use of the pedals – especially harsh acceleration (and usually paired with harsh braking).

Quick Scoop

When people ask “what’s most likely to increase fuel consumption,” most driver training and theory-test style sources give the same answer:
Harsh acceleration and harsh braking.

Why?

  • Rapid acceleration dumps extra fuel into the engine to create a sudden surge of power.
  • Hard braking then throws away all the energy you just used fuel to create, as heat in the brakes.
  • You then have to accelerate again to get back up to speed, repeating the waste cycle.

Several driving-efficiency guides and test-prep blogs explain that these two habits together are the top everyday cause of high fuel use, even more significant than things like air‑conditioning or extra weight for typical drivers.

How harsh driving burns more fuel

Think of your car like this: every time you press the accelerator hard, you’re asking the engine for a big burst of power, and power costs fuel.

  • Harsh acceleration :
    • The engine works at higher load and revs, burning more fuel per second to reach speed quickly.
* Studies and driving-economy articles report that aggressive driving (rapid acceleration, speeding, hard braking) can cut fuel economy by around 30% or more on the highway.
  • Harsh braking :
    • Braking doesn’t directly burn fuel, but it wastes the kinetic energy you just paid for with fuel.
* After a hard stop, you need extra fuel to accelerate back to the previous speed again.

Put together, this “launch–slam–launch” style is a constant cycle of spending fuel and then throwing the benefit away.

Other big contributors (but usually second place)

Even though harsh acceleration/braking is the top “most likely” answer, a few other factors are also important in real life:

  • High speed driving – Fuel use rises quickly with speed because of aerodynamic drag; higher speeds mean the engine is working harder just to hold the same speed.
  • Heavy vehicle weight / towing – More mass means more energy (fuel) needed to get moving and to climb hills.
  • Air‑conditioning use – AC can increase fuel consumption by up to about 20% in some conditions, especially in city driving with lots of stop‑start.
  • Poor maintenance (e.g., badly under‑inflated tyres, some engine faults) – These can raise rolling resistance or make the engine run less efficiently, bumping up fuel use noticeably.

These matter, but for theory-test style questions or general advice, driving style – in particular harsh acceleration and braking – is treated as the main culprit.

Mini takeaway for your post

If you’re writing this up as a short “Quick Scoop” section, you can frame it like:

The habit most likely to increase fuel consumption isn’t your air‑con or a bit of extra luggage – it’s your right foot.
Rapid acceleration and hard braking force the engine to work much harder, then throw away the energy you just paid for in fuel. Smooth, steady driving keeps your tank – and your wallet – fuller for longer.

Bottom note (as requested):
Information gathered from public forums or data available on the internet and portrayed here.