There’s a dramatic piece of good news for electric vehicles, but for the moment, it’s balanced on a knife edge.

That’s according to a new study published in the journal Applied Energy, which explains that over four years, the total cost of ownership is lower for electric cars than for gas guzzlers in Texas, California, and the U.K. The analysis, which takes into account purchase price and depreciation, as well as costs like fuel and maintenance, shows a particularly stark difference in the U.K, where cost of ownership for an electric vehicle is 10 percent less than that for a gasoline car.

The results also show that hybrid vehicles are more expensive than their all-gas counterparts in America and the U.K. That’s because while the cars may be more fuel-efficient than a pure gasoline version, their powertrain suffers from the added expense of batteries and electric motors, as well as the upkeep of a conventional fossil-fuel burner.

The victory for electric cars, however, is very vulnerable to policy changes. Their price advantage is still due to government subsidies, which exist to incentivize their adoption. And in America, at least, there are concerns that the Trump administration may at some point cut tax breaks that currently make buying an electric vehicle a shrewd move.

Still, there’s a glimmer of hope, even if it is some way off. Speaking to the Guardian, the researchers behind the analysis say that thanks in large part to the falling price of batteries, electric cars may be cheaper than gas equivalents even without incentives by 2025.