Car-sharing service Zipcar brought in $55 million in its third quarter this year, up 46 percent from the same quarter a year ago when it made about $38 million in revenue, according to the company’s most recent filing with the Securities and Exchange Commission.

Zipcar is essentially a streamlined car rental service that lets people rent cars by the hour. It’s available in most cities where the cars are strewn across the city in special parking spots. Users sign up and then schedule a time and a car to pick up through the company’s website. They receive a card that activates the car and are free to drive it during their scheduled time.

Zipcar still lost $2.5 million in its last quarter. The company hasn’t been profitable since the fourth quarter last year, when it made $1.3 million off $36 million in revenue. That was also the only quarter the company hasn’t lost money going back to its first quarter of 2008. Most of the cost has come from “fleet operations,” the cost of the company’s staff and maintaining leases and expenses for vehicles.

But its revenue has been steadily increasing. It made about $58 million in 2007, about $84 million in 2008, and brought in $131 million last year. The company has posted around 40 percent year-over-year growth each quarter this year.

The company’s been on a bit of a spending spree, which materializes as a loss on its balance sheets. Zipcar most recently picked up London car-sharing service Streetcar and acquired a minority stake in Spanish car-sharing service Avancar. Zipcar also acquired American rival Flexcar in 2007. The expansions have been funded by a healthy dose of venture capital. To date, the Cambridge, Mass.-based company has raised $59 million to finance its operations.

The company filed to go public earlier this year in order to raise $75 million. The funding was intended to help spin up their operations and pay off debt. To get around the slight losses each quarter Zipcar has also gone through six rounds of funding. It recently closed a round of funding worth $21 million to help pad its balance sheet before it finally goes public sometime next year.