Volvo's plug-in hybrids are steadily gaining market share. As part of its monthly sales recap, the automaker announced Monday that plug-in hybrids accounted for 20.8% of its United States sales in May.

The number was even higher in California, where plug-in hybrids accounted for 47.7% of Volvo's U.S. sales in May.

The national sales figures mean Volvo has achieved the goal it announced just last year, when plug-in hybrids represented about 5% of its U.S. sales. The automaker has made a push to grow plug-in hybrid sales, something it views as an essential step toward widespread adoption of all-electric cars.

Volvo gave its plug-in hybrids a big price reduction, started hiding its tailpipes, and also introduced a program that will pay U.S. owners for plugging in. That's important, as plug-in hybrids can't achieve their potential emissions reductions without getting regularly charged.

2022 Volvo XC60

2022 Volvo XC60

The automaker also just cycled through most of its plug-in hybrid lineup, adding longer electric range to certain models for the European market.

Sales figures quoted here include the all-electric XC40 Recharge as well, as Volvo now puts all vehicles with plugs under the "Recharge" banner. However, it's impossible to tell what share of Volvo's total plug-in car sales that single model accounted for, because Volvo doesn't break out Recharge sales numbers from gasoline XC40 models.

The XC40 Recharge is Volvo's only current all-electric model, but a C40 Recharge is on the way. In comparison, Volvo currently offers plug-in hybrid versions of the S60 and S90 sedans, V60 and V90 wagons, and XC60 and XC90 crossovers.

Farther off, Volvo plans to build the next-generation XC90 with two different platforms underneath—including a skateboard EV platform that will allow the same package inside and out.