GREENWOOD VILLAGE, Colo. (AP) — The parent of national medical transport company American Medical Response said Monday it will buy Doctor's Ambulance Service, which holds emergency-service contracts in Orange County, Calif.

AMR's parent, Emergency Medical Services Corp., did not disclose the terms of the deal but said the purchase would add $18 million a year in annual revenue.

Emergency Medical, which is based in Greenwood, Colo., had revenue in 2009 of $654.3 million. AMR's 17,000 medics and other professionals transport more than 4 million patients each year, according to the company's website.

The sale is expected to close within three months.

Doctor's Ambulance was founded in 1974 and transports about 32,000 patients a year in Orange County. Emergency Medical said Doctor's will continue to operate under the Doctor's brand.

In addition to American Medical Response, which offers ambulance service in 38 states and Washington, D.C., Emergency Medical owns EmCare, an outsourced physician-services business.

Shares of Emergency Medical rose 22 cents to close at $53.14.