Over a little more than a year, General Motors (GM) has seen growing interest in Maven, its on-demand ride-sharing service. The program is already available in 17 cities across the U.S. and Canada, but up to this point the service was limited to rentals on an hourly basis. Now the auto maker is adding a new plan with a longer-term rental option.

Called Reserve, it’s a monthly fee-based plan that lets customers hold onto either a Chevrolet Tahoe or an extended-range electric Chevrolet Volt for 28 days. The per-month price varies depending on the vehicle, with the former priced at $1,500 and the latter at $1,100. But included in each reservation is parking, insurance, and $100 worth of gas.

Maven’s Reserve will only be available in San Francisco and Los Angeles to start, although there are plans to extend into other cities.

“At Maven, we’ve matured our platform to meet the dynamic lifestyle needs of our members through multiple sharing solutions,” said Julia Steyn, vice president of GM’s urban mobility and Maven division in a statement. “Maven Reserve is an innovative approach that answers requests from members for longer-term reservation options.”

Launched in 2016, Maven competes against Zipcar, Getaround, Carma, and traditional car rental services, such as Enterprise, Hertz, Avis, and Budget. In order to put its best foot forward, GM is offering the newer models of its vehicles, giving customers access to Apple CarPlay, Android Auto, OnStar, SiriusXM, and 4G LTE wireless connectivity. The aim is to promote vehicle access whenever and however customers want it.

“Maven Reserve helps our members be there for the moments that matter most, both personally and professionally,” said Megan Stooke, GM’s chief marketing officer for Maven. “Car sharing is evolving and Maven will continue to adapt to members’ wants and needs.”

While it might have been possible to continuously extend a short-term Maven rental for as long as 28 days, it would have been prohibitively expensive. Now, with Reserve, getting things done while testing out a car for a week or a month doesn’t have to break the bank.

To date, more than 25,000 people have signed up for Maven and have made more than 32,000 reservations. The average reservation is for more than 12 hours.