The cost of charging an EV versus refueling a gas vehicle is illustrated in these charts.

• Electricity prices have increased in certain regions of the U.S. due to the rise in gas prices following Russia's invasion of Ukraine, particularly in areas where Tesla's EVs are popular.
• Is it still true that refueling an EV is much cheaper? CNBC analyzed the costs.

For many years, it has been more cost-effective to recharge an electric vehicle than to refuel one with an internal-combustion engine, mile for mile.

While Tesla and other EV makers have profited from the high gas prices, the current situation presents a challenge as electricity prices have also increased, particularly in regions where Tesla's EVs are popular.

Is it still true that refueling an EV is much cheaper? The charts below show how the cost to add 100 miles of range to an average EV or internal-combustion vehicle has changed in different markets over time, helping us determine the answer.

The first chart presents a national average, while the subsequent charts focus on Boston and San Francisco, two cities with high EV popularity and above-average electricity costs.

Despite regional increases in electricity prices, it is still more expensive to refuel your gas tank than to charge your EV's battery.

Over the past few months, the cost of adding 100 miles of range in an internal-combustion vehicle has increased relative to charging an EV an equivalent amount, despite electricity rates keeping pace with gas price increases in Boston and San Francisco.

Although oil prices are predicted to decrease in the near future due to increased production, it is unlikely that the cost of electricity will increase significantly enough to make electric vehicles less cost-effective than internal combustion engines over their entire lifespan.

David Kelley, an analyst at Jeffries, recently calculated that the total lifetime cost of ownership of an EV is approximately $4,700 less than that of an internal-combustion vehicle, based on February data. He predicts that this cost difference will likely increase as more EVs enter the market and battery prices continue to decline in the coming years.

How we crunched the numbers

We had three questions in mind when we put together these charts:

• What is the cost of increasing the range of an average ICE vehicle and an average EV by 100 miles?
• What were the costs three years ago, in February 2019, before the pandemic?
• How have those costs varied between different parts of the U.S.?

In 2020, the Environmental Protection Agency reported that the average new vehicle sold in the U.S. had a combined fuel-economy rating of 25.7 miles per gallon. This means that driving 100 miles in that average vehicle would use 3.9 gallons of gas. However, figures for 2021 have not been released yet.

The EPA's efficiency rating for EVs, known as "MPGe," provides consumers with an idea of how far an EV can travel on 33.7 kilowatt-hours (kWh) of charge. This is equivalent to the energy in a gallon of regular gasoline.

Using 34.7 kWh of electricity to drive 100 miles in a 2022-model-year EV sold in the U.S. would result in an average MPGe rating of about 97.

The graphs show the fluctuations in the cost of 3.9 gallons of gas compared to 34.7 kWh from February 2019 to February 2022, based on monthly data from the U.S. Energy Information Administration and the U.S. Bureau of Labor Statistics.

—CNBC’s Crystal Mercedes contributed to this article.