Panther Express is a two year old company founded by former executives from online advertising network DoubleClick. It has just raised $15.75 million from new investor Index Ventures, and existing investors Gold Hill Capital and Greylock Partners.

The New York company offers content deliver network services to more than 250 large customers, such as The New York Times, and previously raised $6 million in 2006 (our coverage).

Content delivery networks cache content on servers around the world, typically for large web sites. Panther says it is able to spread traffic across more than 15 ISPS to preclude the risk of a service failure at any one point. Its software monitors which servers to send traffic to, and claims to over low prices to customers.

Competitors include Akamai, and others.