Sharing spectrum has emerged as a promising way to meet the exploding demand for wireless data services. In this paper, we consider a scenario in which spectrum is shared between a primary and multiple secondary service providers, all of which are competing for a common pool of customers. We adopt a similar model to one used in earlier work to study competition with unlicensed spectrum, in which users select service providers based on the sum of a congestion cost and the price announce by the service provider. Competition with unlicensed spectrum was shown to potentially decrease social welfare. In contrast, with shared spectrum, we show here that social welfare is always non-decreasing, although the welfare of the primary provider can decrease. Various models of user demand and congestion costs are considered.