What is Overselling?

Overselling, also known as oversubscription, is a business strategy common in shared hosting and low-cost virtual private server (VPS) environments. Providers sell more total capacity (such as bandwidth, disk space, RAM, or CPU cores) than the underlying hardware can physically deliver if every customer used their allocated maximum at the same time. This practice relies on statistical multiplexing: most customers use only a fraction of their allotted resources most of the time.

Providers monitor aggregate usage and overprovision based on historical averages. For example, a server with a 1 Gbps uplink might be sold to 100 customers, each with a 100 Mbps bandwidth cap, expecting average utilization to stay well below 1 Gbps. If too many customers experience simultaneous traffic spikes, performance degrades for everyone. Overselling allows low prices but introduces risk of oversaturation during peak demand. Premium hosting providers often guarantee dedicated resources or enforce strict per-customer limits to avoid this.

In the wider hosting stack, overselling is a trade-off between cost and reliability. It is closely related to concepts like contention ratio, burstable billing, and quality of service. In cloud computing, overselling is less common due to resource isolation and pay-per-use models, though some cloud providers still overcommit CPU or memory based on similar assumptions.